Index: modules/system/system.module
===================================================================
--- modules/system/system.module	(revision 1)
+++ modules/system/system.module	(working copy)
@@ -847,8 +847,8 @@
   $form['site_offline_message'] = array(
     '#type' => 'textarea',
     '#title' => t('Site off-line message'),
-    '#default_value' => variable_get('site_offline_message', t('@site is currently under maintenance. We should be back shortly. Thank you for your patience.', array('@site' => variable_get('site_name', t('This Drupal site'))))),
-    '#description' => t('Message to show visitors when the site is in off-line mode.')
+    '#default_value' => variable_get('site_offline_message', t('!site is currently under maintenance. We should be back shortly. Thank you for your patience.')),
+    '#description' => t('Message to show visitors when the site is in off-line mode.') .' '. t('Available variables are:') .' !site, !uri, !uri_brief, !mailto, !date.'
   );
 
   return system_settings_form($form);
Index: includes/common.inc
===================================================================
--- includes/common.inc	(revision 1)
+++ includes/common.inc	(working copy)
@@ -310,10 +310,20 @@
  * Generates a site off-line message
  */
 function drupal_site_offline() {
+  global $base_url;
+
   drupal_set_header('HTTP/1.0 503 Service unavailable');
   drupal_set_title(t('Site off-line'));
-  print theme('maintenance_page', filter_xss_admin(variable_get('site_offline_message',
-    t('@site is currently under maintenance. We should be back shortly. Thank you for your patience.', array('@site' => variable_get('site_name', t('This Drupal site')))))));
+  $variables = array(
+    '!site' => variable_get('site_name', 'Drupal'),
+    '!uri' => $base_url,
+    '!uri_brief' => substr($base_url, strlen('http://')),
+    '!mailto' => variable_get('site_mail', ini_get('sendmail_from')),
+    '!date' => format_date(time()),
+  );
+
+  $site_offline_message = variable_get('site_offline_message', t('!site is currently under maintenance. We should be back shortly. Thank you for your patience.'));
+  print theme('maintenance_page', strtr(filter_xss_admin($site_offline_message), $variables));
 }
 
 /**