Gmail adds undo-send-email in labs
How many times have you sent an email message and immediately wished you didn’t?
Gmail has added a feature that people have been requesting for ages. If you enable the feature (in labs), it adds a 5 second delay to your emails being sent. During the delay, you have the option to undo the email being sent (Awesomeness).
I have to wonder how long it’s going to be before other webmail services copy this feature.