The Gmail Second Thought Feature

CNN has a nice write-up on what to do when you send an ill-advised email via Gmail. It is not a perfect solution, but...

The ability to "undo" an e-mail has been a little known feature of Google's e-mail service since last year. But in the past few days, it appears to have been improved

Google Operating System, an unofficial blog that shares Google news and tips, noted this weekend that a user now has up to 30 seconds to take back an unfortunate message.
In reality, the feature doesn't actually pull back an e-mail that's already gone, it simply holds your message for 30 seconds before sending it out -- just in case you change your mind.