Debugging cron tasks in WordPress
I found the wp-cron dashboard pluginhttp://wordpress.org/extend/plugins/wp-cron-dashboard/very helpful. Using it I was able to see what cron tasks were working or not.
I also found that the docs on the cron functions weren't very clear. When setting up a wp cron task make sure you add the function as an action using add_action only then can you run wp_schedule_event on the task.
Good luck!