Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.756
diff -u -p -r1.756 common.inc
--- includes/common.inc	30 Jan 2008 23:07:41 -0000	1.756
+++ includes/common.inc	13 Feb 2008 20:44:15 -0000
@@ -362,7 +362,7 @@ function drupal_not_found() {
   }
 
   // To conserve CPU and bandwidth, omit the blocks.
-  print theme('page', $return, FALSE);
+  print theme('page', $return, variable_get('site_404_blocks', FALSE));
 }
 
 /**
Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.63
diff -u -p -r1.63 system.admin.inc
--- modules/system/system.admin.inc	4 Feb 2008 12:35:48 -0000	1.63
+++ modules/system/system.admin.inc	13 Feb 2008 20:44:16 -0000
@@ -1223,6 +1223,14 @@ function system_error_reporting_settings
     '#field_prefix' => url(NULL, array('absolute' => TRUE)) . (variable_get('clean_url', 0) ? '' : '?q=')
   );
 
+  $form['site_404_blocks'] = array(
+    '#type' => 'radios',
+    '#title' => t('Display blocks on 404 (not found) page'),
+    '#default_value' => variable_get('site_404_blocks', 0),
+    '#options' => array(TRUE => t('Enable'), FALSE => t('Disable')),
+    '#description' => t('If enabled then a 404 (not found) page will be fully themed.  If disabled then a 404 (not found) page will not display the blocks.  The suggested reason for leaving this disabled is for performance concerns.  This option is only valid if you provide a "Default 404 (not found) page".')
+  );
+
   $form['error_level'] = array(
     '#type' => 'select', '#title' => t('Error reporting'), '#default_value' => variable_get('error_level', 1),
     '#options' => array(t('Write errors to the log'), t('Write errors to the log and to the screen')),