Index: wp-includes/bookmark.php
===================================================================
--- wp-includes/bookmark.php	(revision 18536)
+++ wp-includes/bookmark.php	(working copy)
@@ -105,6 +105,8 @@
  *		separated by commas.
  * 'exclude' - Default is empty string (string). Exclude other categories
  *		separated by commas.
+ * 'expiration' - Default is 600 (integer). Lifetime of result cache when ordering
+ *		by 'rand'
  *
  * @since 2.1.0
  * @uses $wpdb Database Object
@@ -121,15 +123,19 @@
 		'limit' => -1, 'category' => '',
 		'category_name' => '', 'hide_invisible' => 1,
 		'show_updated' => 0, 'include' => '',
-		'exclude' => '', 'search' => ''
+		'exclude' => '', 'search' => '',
+		'expire' => 60
 	);
 
 	$r = wp_parse_args( $args, $defaults );
 	extract( $r, EXTR_SKIP );
-
+	
 	$cache = array();
 	$key = md5( serialize( $r ) );
-	if ( $cache = wp_cache_get( 'get_bookmarks', 'bookmark' ) ) {
+	if ( $orderby == 'rand' ) {
+		if( $results = wp_cache_get( $key, 'get_bookmarks_rand' ) )
+			return apply_filters('get_bookmarks', $results, $r );
+	} elseif ( $cache = wp_cache_get( 'get_bookmarks', 'bookmark' ) ) {
 		if ( is_array($cache) && isset( $cache[ $key ] ) )
 			return apply_filters('get_bookmarks', $cache[ $key ], $r );
 	}
@@ -252,8 +258,12 @@
 
 	$results = $wpdb->get_results($query);
 
-	$cache[ $key ] = $results;
-	wp_cache_set( 'get_bookmarks', $cache, 'bookmark' );
+	if(	$orderby == 'rand()' ) {
+		wp_cache_set( $key, $results, 'get_bookmarks_rand', $expire );
+	} else {
+		$cache[ $key ] = $results;
+		wp_cache_set( 'get_bookmarks', $cache, 'bookmark' );
+	}
 
 	return apply_filters('get_bookmarks', $results, $r);
 }