No, it’s still working for me and for others as well.
Please look into logs & error messages, otherwise I cannot help.
UpTimeRobot.com
Pre-cache I belief works with Wp-Cron, which is triggered by traffic/site visits. No traffic, no Cron.
Signup for a Free account to get http traffic. Or Google Cpanel WordPress Cron Job..
As a side note with regards to wp-cron requiring traffic, you can also set it up as a regular cron job (I’ve done some myself) which takes out the traffic requirement. See http://support.hostgator.com/articles/specialized-help/technical/wordpress/how-to-replace-wordpress-cron-with-a-real-cron-job
