--- devel.module
+++ (clipboard)
@@ -551,12 +551,15 @@
 }
 
 function devel_block_switch_user() {
-  $links = devel_switch_user_list();
-  if (!empty($links)) {
-    $block['subject'] = t('Switch user');
-    $block['content'] = theme('links', $links);
-    $block['content'] .= drupal_get_form('devel_switch_user_form');
-    return $block;
+  if (user_access('switch users')) {
+    $list_size = variable_get('devel_switch_user_list_size', 10);
+    $links = devel_switch_user_list();
+    if (!empty($links) or $list_size == 0) {
+      $block['subject'] = t('Switch user');
+      $block['content'] = theme('links', $links);
+      $block['content'] .= drupal_get_form('devel_switch_user_form');
+      return $block;
+    }
   }
 }