--- modules/system/system.admin.inc 2010-01-11 11:15:37.000000000 +0100
+++ modules/system/system.admin.inc 2010-01-11 11:15:03.000000000 +0100
@@ -1955,7 +1955,7 @@ function system_date_time_settings() {
 
       $choices = array();
       foreach ($formats as $f => $format) {
-        $choices[$f] = format_date(REQUEST_TIME, 'custom', $f);
+        $choices[$f] = system_date_time_get_ui_text($format);
       }
       $default = variable_get('date_format_' . $type, array_shift(array_keys($formats)));
 
@@ -1991,6 +1991,26 @@ function system_date_time_settings() {
 }
 
 /**
+ * Return descriptive text to disambiguate date format choices.
+ */
+function system_date_time_get_ui_text($format = array()) {
+  if (isset($format['format'])) {
+    $format_text = format_date(REQUEST_TIME, 'custom', $format['format']);
+    // Only add descriptive UI text for short formats.
+    if ($format['type'] != 'long') {
+      // Append example time of 2:30pm on 28th of current month.
+      $example_date = getdate(REQUEST_TIME);
+      $example_timestamp = mktime(14, 30, 59, $example_date['mon'], 28, $example_date['year']);
+      $format_text .= ' (e.g. ' . format_date($example_timestamp, 'custom', $format['format']) . ')';
+    }
+    return $format_text;
+  }
+  else { // No format supplied.
+    return FALSE;
+  }
+}
+
+/**
  * Theme function for date settings form.
  *
  * @ingroup themeable
@@ -2070,7 +2090,7 @@ function system_add_date_format_type_for
   }
   $choices = array();
   foreach ($formats as $f => $format) {
-    $choices[$f] = format_date(REQUEST_TIME, 'custom', $f);
+    $choices[$f] = system_date_time_get_ui_text($format);
   }
   // Show date format select list.
   $form['date_format'] = array(