diff --git includes/common.inc includes/common.inc
index 701c32c..d2d45ff 100644
--- includes/common.inc
+++ includes/common.inc
@@ -5468,6 +5468,24 @@ function entity_get_controller($entity_type) {
 }
 
 /**
+ * Properly handle multistep behavior on entity forms.
+ *
+ * This sets takes the current form values, builds a proper entity object out
+ * of them and stores this entity object in $form_state['ENTITY_TYPE'].
+ *
+ * Note that the #entity_type property is required to be set to a valid entity
+ * type.
+ */
+function entity_submit_multistep_form($form, &$form_state) {
+  $entity_type = $form['#entity_type'];
+  $entity = entity_get_controller($entity_type)->submitFormValues($form, $form_state);
+
+  $form_state[$entity_type] = $entity;
+  $form_state['rebuild'] = TRUE;
+  return $entity;
+}
+
+/**
  * Performs one or more XML-RPC request(s).
  *
  * @param $url
diff --git includes/entity.inc includes/entity.inc
index 66b1eb4..2596ae5 100644
--- includes/entity.inc
+++ includes/entity.inc
@@ -38,6 +38,25 @@ interface DrupalEntityControllerInterface {
    *   An array of entity objects indexed by their ids.
    */
   public function load($ids = array(), $conditions = array());
+
+  /**
+   * Build an entity by processing a submitted entity form.
+   *
+   * This also stores a copy of the built entity in $form_state['ENTITY_TYPE'],
+   * which is required for multi-step forms.
+   *
+   * @return
+   *   An entity that is ready to be saved.
+   */
+  public function submitFormValues($form, &$form_state);
+
+   /**
+   * Build an entity by processing an array of values.
+   *
+   * @return
+   *   An entity that is ready to be saved.
+   */
+  public function submit($values);
 }
 
 /**
@@ -291,4 +310,18 @@ class DrupalDefaultEntityController implements DrupalEntityControllerInterface {
   protected function cacheSet($entities) {
     $this->entityCache += $entities;
   }
+
+  public function submitFormValues($form, &$form_state) {
+    // Actually submit the form values.
+    $entity = $this->submit($form_state['values']);
+
+    field_attach_submit($this->entityType, $entity, $form, $form_state);
+
+    return $entity;
+  }
+
+  public function submit($values) {
+    $entity = (object) $values;
+    return $entity;
+  }
 }
diff --git modules/comment/comment.module modules/comment/comment.module
index 9513ca8..066c84a 100644
--- modules/comment/comment.module
+++ modules/comment/comment.module
@@ -1492,6 +1492,35 @@ class CommentController extends DrupalDefaultEntityController {
       $comments[$key] = $comment;
     }
   }
+
+  public function submit($comment) {
+    $comment += array('subject' => '');
+    if (!isset($comment['date'])) {
+      $comment['date'] = 'now';
+    }
+
+    $comment['timestamp'] = strtotime($comment['date']);
+    if (isset($comment['author'])) {
+      $account = user_load_by_name($comment['author']);
+      $comment['uid'] = $account->uid;
+      $comment['name'] = $comment['author'];
+    }
+
+    // Validate the comment's subject. If not specified, extract from comment body.
+    if (trim($comment['subject']) == '') {
+      // The body may be in any format, so:
+      // 1) Filter it into HTML
+      // 2) Strip out all HTML tags
+      // 3) Convert entities back to plain-text.
+      $comment['subject'] = truncate_utf8(trim(decode_entities(strip_tags(check_markup($comment['comment'], $comment['comment_format'])))), 29, TRUE);
+      // Edge cases where the comment body is populated only by HTML tags will
+      // require a default subject.
+      if ($comment['subject'] == '') {
+        $comment['subject'] = t('(No subject)');
+      }
+    }
+    return (object)$comment;
+  }
 }
 
 /**
@@ -1629,11 +1658,13 @@ function comment_form($form, &$form_state, $comment) {
   $comment = (array) $comment;
   // Take into account multi-step rebuilding.
   if (isset($form_state['comment'])) {
-    $comment = $form_state['comment'] + (array) $comment;
+    $comment = (array) $form_state['comment'] + (array) $comment;
   }
   $comment += array('name' => '', 'mail' => '', 'homepage' => '');
   $comment = (object) $comment;
 
+  $form['#entity_type'] = 'comment';
+
   if (isset($form_state['comment_preview'])) {
     $form += $form_state['comment_preview'];
   }
@@ -1863,7 +1894,6 @@ function comment_form($form, &$form_state, $comment) {
   }
 
   $comment->node_type = 'comment_node_' . $node->type;
-  $form['#builder_function'] = 'comment_form_submit_build_comment';
   field_attach_form('comment', $comment, $form, $form_state);
 
   return $form;
@@ -1873,8 +1903,8 @@ function comment_form($form, &$form_state, $comment) {
  * Build a preview from submitted form values.
  */
 function comment_form_build_preview($form, &$form_state) {
-  $comment = comment_form_submit_build_comment($form, $form_state);
-  $form_state['comment_preview'] = comment_preview($comment);
+  entity_submit_multistep_form($form, $form_state);
+  $form_state['comment_preview'] = comment_preview($form_state['comment']);
 }
 
 /**
@@ -2000,51 +2030,11 @@ function comment_form_validate($form, &$form_state) {
 }
 
 /**
- * Prepare a comment for submission.
- *
- * @param $comment
- *   An associative array containing the comment data.
- */
-function comment_submit($comment) {
-  $comment += array('subject' => '');
-  if (!isset($comment['date'])) {
-    $comment['date'] = 'now';
-  }
-
-  $comment['timestamp'] = strtotime($comment['date']);
-  if (isset($comment['author'])) {
-    $account = user_load_by_name($comment['author']);
-    $comment['uid'] = $account->uid;
-    $comment['name'] = $comment['author'];
-  }
-
-  // Validate the comment's subject. If not specified, extract from comment body.
-  if (trim($comment['subject']) == '') {
-    // The body may be in any format, so:
-    // 1) Filter it into HTML
-    // 2) Strip out all HTML tags
-    // 3) Convert entities back to plain-text.
-    $comment['subject'] = truncate_utf8(trim(decode_entities(strip_tags(check_markup($comment['comment'], $comment['comment_format'])))), 29, TRUE);
-    // Edge cases where the comment body is populated only by HTML tags will
-    // require a default subject.
-    if ($comment['subject'] == '') {
-      $comment['subject'] = t('(No subject)');
-    }
-  }
-  return (object)$comment;
-}
-
-/**
- * Build a comment by processing form values and prepare for a form rebuild.
+ * Build a comment by processing submitted form values and prepare for a form rebuild.
  */
-function comment_form_submit_build_comment($form, &$form_state) {
-  $comment = comment_submit($form_state['values']);
-
-  field_attach_submit('comment', $comment, $form, $form_state);
-
-  $form_state['comment'] = (array)$comment;
-  $form_state['rebuild'] = TRUE;
-  return $comment;
+function comment_submit_form_values($form, &$form_state) {
+  $node = entity_get_controller('comment')->submitFormValues($form, $form_state);
+  return $node;
 }
 
 /**
@@ -2052,7 +2042,7 @@ function comment_form_submit_build_comment($form, &$form_state) {
  */
 function comment_form_submit($form, &$form_state) {
   $node = node_load($form_state['values']['nid']);
-  $comment = comment_form_submit_build_comment($form, $form_state);
+  $comment = comment_submit_form_values($form, $form_state);
   if (user_access('post comments') && (user_access('administer comments') || $node->comment == COMMENT_NODE_OPEN)) {
     comment_save($comment);
     // Explain the approval queue if necessary.
diff --git modules/field/field.form.inc modules/field/field.form.inc
index f068ed5..8839830 100644
--- modules/field/field.form.inc
+++ modules/field/field.form.inc
@@ -327,15 +327,12 @@ function field_default_form_errors($obj_type, $object, $field, $instance, $langc
  */
 function field_add_more_submit($form, &$form_state) {
   // Set the form to rebuild and run submit handlers.
-  if (isset($form['#builder_function']) && function_exists($form['#builder_function'])) {
-    $entity = $form['#builder_function']($form, $form_state);
-
-    // Make the changes we want to the form state.
-    $field_name = $form_state['clicked_button']['#field_name'];
-    $langcode = $form_state['clicked_button']['#language'];
-    if ($form_state['values'][$field_name . '_add_more']) {
-      $form_state['field_item_count'][$field_name] = count($form_state['values'][$field_name][$langcode]);
-    }
+  entity_submit_multistep_form($form, $form_state);
+  // Make the changes we want to the form state.
+  $field_name = $form_state['clicked_button']['#field_name'];
+  $langcode = $form_state['clicked_button']['#language'];
+  if ($form_state['values'][$field_name . '_add_more']) {
+    $form_state['field_item_count'][$field_name] = count($form_state['values'][$field_name][$langcode]);
   }
 }
 
diff --git modules/node/node.module modules/node/node.module
index a0c215e..218b02d 100644
--- modules/node/node.module
+++ modules/node/node.module
@@ -822,24 +822,8 @@ function node_validate($node, $form = array()) {
 /**
  * Prepare node for save and allow modules to make changes.
  */
-function node_submit($node) {
-  global $user;
-
-  // Convert the node to an object, if necessary.
-  $node = (object)$node;
-
-  if (user_access('administer nodes')) {
-    // Populate the "authored by" field.
-    if ($account = user_load_by_name($node->name)) {
-      $node->uid = $account->uid;
-    }
-    else {
-      $node->uid = 0;
-    }
-  }
-  $node->created = !empty($node->date) ? strtotime($node->date) : REQUEST_TIME;
-  $node->validated = TRUE;
-
+function node_submit($values) {
+  $node = entity_get_controller('node')->submit($values);
   return $node;
 }
 
@@ -3073,4 +3057,38 @@ class NodeController extends DrupalDefaultEntityController {
     $this->hookLoadArguments[] = array_keys($typed_nodes);
     parent::attachLoad($nodes);
   }
+
+  public function submitFormValues($form, &$form_state) {
+    // Unset any button-level handlers, execute all the form-level submit
+    // functions to process the form values into an updated node.
+    // TODO: This is ugly to have here. To be able to remove these two lines,
+    // we have to standaridze the various entity types to all either use
+    // form-level or button-level submitting to actually save the entity.
+    // Currently, only node.module uses button level submitting to save the
+    // entity while form-level submit handlers are used by other modules to
+    // expand their values in $form_state. The latter could be moved to a
+    // to-be-created hook_ENTITY_TYPE_submit() that is invoked from here.
+    // Alternatively, all other entity types could adopt node.module's way and
+    // use button-level submit handlers to save the entity.
+    unset($form_state['submit_handlers']);
+    form_execute_handlers('submit', $form, $form_state);
+    return parent::submitFormValues($form, $form_state);
+  }
+
+  public function submit($values) {
+    $node = parent::submit($values);
+    if (user_access('administer nodes')) {
+      // Populate the "authored by" field.
+      if ($account = user_load_by_name($node->name)) {
+        $node->uid = $account->uid;
+      }
+      else {
+        $node->uid = 0;
+      }
+    }
+    $node->created = !empty($node->date) ? strtotime($node->date) : REQUEST_TIME;
+    $node->validated = TRUE;
+
+    return $node;
+  }
 }
diff --git modules/node/node.pages.inc modules/node/node.pages.inc
index 5b19fe8..3be2f29 100644
--- modules/node/node.pages.inc
+++ modules/node/node.pages.inc
@@ -111,10 +111,7 @@ function node_form($form, &$form_state, $node) {
   global $user;
 
   if (isset($form_state['node'])) {
-    $node = $form_state['node'] + (array)$node;
-  }
-  if (isset($form_state['node_preview'])) {
-    $form['#prefix'] = $form_state['node_preview'];
+    $node = (array)$form_state['node'] + (array)$node;
   }
   $node = (object)$node;
   foreach (array('title') as $key) {
@@ -129,6 +126,13 @@ function node_form($form, &$form_state, $node) {
     $node->in_preview = TRUE;
   }
 
+  if (isset($form_state['node_preview'])) {
+    $form['#prefix'] = $form_state['node_preview'];
+  }
+
+  // Set the entity type for field and entity APIs.
+  $form['#entity_type'] = 'node';
+
   // Set the id and identify this as a node edit form.
   $form['#id'] = 'node-form';
   $form['#node_edit_form'] = TRUE;
@@ -290,7 +294,6 @@ function node_form($form, &$form_state, $node) {
   $form['#validate'][] = 'node_form_validate';
   $form['#theme'] = array($node->type . '_node_form', 'node_form');
 
-  $form['#builder_function'] = 'node_form_submit_build_node';
   field_attach_form('node', $node, $form, $form_state, $node->language);
 
   return $form;
@@ -311,8 +314,8 @@ function node_form_delete_submit($form, &$form_state) {
 
 
 function node_form_build_preview($form, &$form_state) {
-  $node = node_form_submit_build_node($form, $form_state);
-  $form_state['node_preview'] = node_preview($node);
+  entity_submit_multistep_form($form, $form_state);
+  $form_state['node_preview'] = node_preview($form_state['node']);
 }
 
 /**
@@ -404,9 +407,7 @@ function theme_node_preview($node) {
 }
 
 function node_form_submit($form, &$form_state) {
-  global $user;
-
-  $node = node_form_submit_build_node($form, $form_state);
+  $node = node_submit_form_values($form, $form_state);
   $insert = empty($node->nid);
   node_save($node);
   $node_link = l(t('view'), 'node/' . $node->nid);
@@ -436,17 +437,8 @@ function node_form_submit($form, &$form_state) {
 /**
  * Build a node by processing submitted form values and prepare for a form rebuild.
  */
-function node_form_submit_build_node($form, &$form_state) {
-  // Unset any button-level handlers, execute all the form-level submit
-  // functions to process the form values into an updated node.
-  unset($form_state['submit_handlers']);
-  form_execute_handlers('submit', $form, $form_state);
-  $node = node_submit($form_state['values']);
-
-  field_attach_submit('node', $node, $form, $form_state);
-
-  $form_state['node'] = (array)$node;
-  $form_state['rebuild'] = TRUE;
+function node_submit_form_values($form, &$form_state) {
+  $node = entity_get_controller('node')->submitFormValues($form, $form_state);
   return $node;
 }
 
diff --git modules/taxonomy/taxonomy.admin.inc modules/taxonomy/taxonomy.admin.inc
index 4507f83..fb1fbd0 100644
--- modules/taxonomy/taxonomy.admin.inc
+++ modules/taxonomy/taxonomy.admin.inc
@@ -682,16 +682,16 @@ function taxonomy_form_term($form, &$form_state, $vocabulary, $edit = array()) {
   );
 
   // Take into account multi-step rebuilding.
-  if (isset($form_state['term'])) {
-    $edit = $form_state['term'] + $edit;
+  if (isset($form_state['taxonomy_term'])) {
+    $edit = (array)$form_state['taxonomy_term'] + $edit;
   }
 
   $parent = array_keys(taxonomy_get_parents($edit['tid']));
+  $form['#entity_type'] = 'taxonomy_term';
   $form['#term'] = $edit;
   $form['#term']['parent'] = $parent;
   $form['#vocabulary'] = $vocabulary;
   $form['#vocabulary']->nodes = drupal_map_assoc($vocabulary->nodes);
-  $form['#builder_function'] = 'taxonomy_form_term_submit_builder';
 
   // Check for confirmation forms.
   if (isset($form_state['confirm_delete'])) {
@@ -820,7 +820,7 @@ function taxonomy_form_term_submit($form, &$form_state) {
     return;
   }
 
-  $term = taxonomy_form_term_submit_builder($form, $form_state);
+  $term = taxonomy_term_submit_form_values($form, $form_state);
 
   $status = taxonomy_term_save($term);
   switch ($status) {
@@ -864,13 +864,8 @@ function taxonomy_form_term_submit($form, &$form_state) {
 /**
  * Build a term by processing form values and prepare for a form rebuild.
  */
-function taxonomy_form_term_submit_builder($form, &$form_state) {
-  $term = (object) $form_state['values'];
-  field_attach_submit('taxonomy_term', $term, $form, $form_state);
-
-  $form_state['term'] = (array)$term;
-  $form_state['rebuild'] = TRUE;
-
+function taxonomy_term_submit_form_values($form, &$form_state) {
+  $term = entity_get_controller('taxonomy_term')->submitFormValues($form, $form_state);
   return $term;
 }