no preview button (how to enable the submit button instead)

Usernode guestbook uses the original comment buttons to post a guestbook entry like a comment. Due to some ugly nesting in preview mode (the preview is rendered like a comment and the comment itself is rendered inside of this again) I disabled the preview mode, because I currently see no well designed solution for this. Our Drupal gurus may know what to do here and I will change this as soon as I know.

Until then it is advised to let users submit comments without previewing. I suppose the problem is that you have set comment previewing to required. So here's my advice:

Recommended configuration

1. Go to admin/content/comment/settings
2. Set "Preview comment" to "Optional"

Please post if it helped you.

Will be fixed in next dev version. Even if preview is required for comments usernode guestbook entries will have a submit button.
Preview is not possible yet due to a rendering problem. We need a more elegant solution for this instead of complete rewrite of the form.

Old or potentially new code is commented out.

/**
 * Implementation of hook_form_alter to change appearence of comment_form
 * especially for usernodes.
 *
 * @param string $form_id
 *   name of the form
 * @param array $form
 *   editable form array by reference
 */
function usernode_guestbook_form_alter($form_id, &$form) {
  if ($form_id == 'comment_form') {
    $node = node_load(array('nid' => $form['nid']['#value']));
    if ($node->type == 'usernode') {
      unset($form['subject']);
      $form['comment_filter']['comment']['#rows'] = 3;
      $form['comment_filter']['comment']['#title'] = t('Leave a message');
      /*
      if (variable_get('comment_preview', COMMENT_PREVIEW_REQUIRED) == COMMENT_PREVIEW_OPTIONAL) {
        unset($form['preview']);
      }
      else {
        $op = isset($_POST['op']) ? $_POST['op'] : '';
        $form['preview']['#value'] = t('Preview');
        if ($op == t('Preview')) {
          $form['#after_build'] = array('comment_form_add_preview');
          $form['submit'] = array('#type' => 'submit', '#value' => t('Submit'), '#weight' => 20);
        }
      }
      */
      // Previewing is ugly because the form is rendered as a comment
      // and preview is rendered inside of this again. Always show submit button.
      unset($form['preview']);
      $form['submit'] = array('#type' => 'submit', '#value' => t('Submit'), '#weight' => 20);
      $form['#redirect'] = _usernode_guestbook_redirect($node->uid, 'comments');
    }
  }
}

committed into latest dev version.