Gmail has added another very good feature which will be loved by many users. With this new “Undo Send” feature you can actually stop an email from being sent to the recipient. You need to act prompt because the “Undo” link will actually appear for just 5 seconds. If you are interested in trying out this feature you can actually enable it from the Gmail Labs section under Settings.
Personally I feel that this is not really a great feature from Gmail. Though it might help us in many situations, 5 seconds is really a very low time frame. Google should have provided a configurable setting which allows the user to set a time delay, say 30 sec or 60 sec, before sending a mail. I hope Google would work on this feature based on the user feedback to provide us with more configurable options.