Gmail Feature: Stop Sending Mail You Later Regret
When you enable Mail Goggles, it will check that you're really sure you want to send that late night Friday email. And what better way to check than by making you solve a few simple math problems after you click send to verify you're in the right state of mind?
It is clever and fills a need when you think about it. They need to find a way to enable this feature on cell phones where it would be more useful...