The benevolent folks over at Google have been kind enough to add a nifty new Undo Send feature to Gmail. To turn on the new feature, go to 'undo send' in Gmail Labs under 'settings.' But be warned: it can't retrieve an email that's already been sent; it just holds onto your message for five seconds "so you have a chance to hit the panic button." In related news, Valleywag has a wish list of five other things that could be undo on the internet.