Topic: What started as an April Fool's

http://gmailblog.blogspot.com/2008/10/new-in-labs-stop-sending-mail-you-later.html

Also, check out the 'Forgotten Attachment Detector'

In your mail, go to Settings, then the far right link is their mail labs. Some pretty good stuff in there

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Any sufficiently advanced bug is indistinguishable from a feature.