Index: wp-admin/includes/nav-menu.php
===================================================================
--- wp-admin/includes/nav-menu.php	(revision 14744)
+++ wp-admin/includes/nav-menu.php	(working copy)
@@ -405,7 +405,10 @@
 	$locations = get_registered_nav_menus();
 	$menus = wp_get_nav_menus();
 	$menu_locations = get_nav_menu_locations();
+	$num_locations = count( array_keys($locations) );
 
+	echo '<p>' . sprintf( _n('Your theme supports %s menu.  Assign a menu to your theme.', 'Your theme supports %s menus. Assign menus to your theme.', $num_locations), number_format_i18n($num_locations) ) . '</p>';
+
 	foreach ( $locations as $location => $description ) {
 		?>
 		<p>