Index: wp-includes/cron.php
===================================================================
--- wp-includes/cron.php	(revision 7916)
+++ wp-includes/cron.php	(working copy)
@@ -1,6 +1,11 @@
 <?php
 
 function wp_schedule_single_event( $timestamp, $hook, $args = array()) {
+	// don't schedule a duplicate if there's already an identical event due in the next 10 minutes
+	$next = wp_next_scheduled($hook, $args);
+	if ( $next && $next <= $timestamp + 600 )
+		return;
+		
 	$crons = _get_cron_array();
 	$key = md5(serialize($args));
 	$crons[$timestamp][$hook][$key] = array( 'schedule' => false, 'args' => $args );