Index: wp-includes/ms-functions.php
===================================================================
--- wp-includes/ms-functions.php	(revision 15155)
+++ wp-includes/ms-functions.php	(working copy)
@@ -159,15 +159,10 @@
 }
 
 function get_most_active_blogs( $num = 10, $display = true ) {
-	$most_active = get_site_option( 'most_active' );
+	$most_active = get_site_transient( 'most_active' );
 	$update = false;
-	if ( is_array( $most_active ) ) {
-		if ( ( $most_active['time'] + 60 ) < time() ) { // cache for 60 seconds.
-			$update = true;
-		}
-	} else {
+	if ( empty( $most_active ) || ! is_array( $most_active ) )
 		$update = true;
-	}
 
 	if ( $update == true ) {
 		unset( $most_active );
@@ -186,7 +181,7 @@
 			unset( $most_active );
 			$most_active = $t;
 		}
-		update_site_option( 'most_active', $most_active );
+		set_site_transient( 'most_active', $most_active, 60 ); // cache for 60 seconds.
 	}
 
 	if ( $display == true ) {