Index: wp-admin/includes/dashboard.php
===================================================================
--- wp-admin/includes/dashboard.php	(revision 18223)
+++ wp-admin/includes/dashboard.php	(working copy)
@@ -1031,30 +1031,37 @@
  */
 function wp_dashboard_cached_rss_widget( $widget_id, $callback, $check_urls = array() ) {
 	$loading = '<p class="widget-loading hide-if-no-js">' . __( 'Loading&#8230;' ) . '</p><p class="hide-if-js">' . __( 'This widget requires JavaScript.' ) . '</p>';
+	$doing_ajax = ( defined('DOING_AJAX') && DOING_AJAX );
 
 	if ( empty($check_urls) ) {
 		$widgets = get_option( 'dashboard_widget_options' );
-		if ( empty($widgets[$widget_id]['url']) ) {
+		if ( empty($widgets[$widget_id]['url']) && ! $doing_ajax ) {
 			echo $loading;
 			return false;
 		}
 		$check_urls = array( $widgets[$widget_id]['url'] );
 	}
 
-	include_once ABSPATH . WPINC . '/class-feed.php';
-	foreach ( $check_urls as $check_url ) {
-		$cache = new WP_Feed_Cache_Transient('', md5($check_url), '');
-		if ( ! $cache->load() ) {
-			echo $loading;
-			return false;
-		}
+	$cache_key = 'dash_' . md5( $callback . implode(',', $check_urls) );
+	if ( false !== ( $output = get_transient( $cache_key ) ) ) {
+		echo $output;
+		return true;
 	}
 
+	if ( ! $doing_ajax ) {
+		echo $loading;
+		return false;
+	}
+
+	ob_start();
+
 	if ( $callback && is_callable( $callback ) ) {
 		$args = array_slice( func_get_args(), 2 );
 		array_unshift( $args, $widget_id );
 		call_user_func_array( $callback, $args );
 	}
+	
+	set_transient( $cache_key, ob_get_flush(), 43200); //Default lifetime in cache of 12 hours
 
 	return true;
 }
Index: wp-admin/index-extra.php
===================================================================
--- wp-admin/index-extra.php	(revision 18223)
+++ wp-admin/index-extra.php	(working copy)
@@ -6,6 +6,8 @@
  * @subpackage Administration
  */
 
+define('DOING_AJAX', true);
+
 /** Load WordPress Bootstrap */
 require_once( './admin.php' );
 
@@ -18,19 +20,19 @@
 switch ( $_GET['jax'] ) {
 
 case 'dashboard_incoming_links' :
-	wp_dashboard_incoming_links_output();
+	wp_dashboard_incoming_links();
 	break;
 
 case 'dashboard_primary' :
-	wp_dashboard_rss_output( 'dashboard_primary' );
+	wp_dashboard_primary();
 	break;
 
 case 'dashboard_secondary' :
-	wp_dashboard_secondary_output();
+	wp_dashboard_secondary();
 	break;
 
 case 'dashboard_plugins' :
-	wp_dashboard_plugins_output();
+	wp_dashboard_plugins();
 	break;
 
 }