Robot Chicken
Seriously?
Mail Goggles!!
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?
By default, Mail Goggles is only active late night on the weekend as that is the time you're most likely to need it. Once enabled, you can adjust when it's active in the General settings.
Hopefully Mail Goggles will prevent many of you out there from sending messages you wish you hadn't. Like that late night memo -- I mean mission statement -- to the entire firm.
http://gmailblog.blogspot.com/2008/10/new-in-labs-stop-sending-mail-you-later.html