Google Mail Goggles
Google wants to help you stop sending email you will regret later with a new tool called Mail Goggles. The idea is to have you answer a few easy math questions which, in theory, will determine whether you are in the right frame of mind to send the email in the first place.
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?