Gmail has added a feature that returns you to the previous screen *immediately* upon pressing send. This means no more waiting until that message is *actually* sent and I love this. The idea is simple and is certainly pervasive in desktop applications: have your interface respond as if the action the user has taken has fully completed, no matter what else needs to happen behind the scenes. By adding the “Background Send” feature to Labs, the user has a faster experience and any delay is pushed out from the interface (which would potentially prevent further user interaction). Speaking from experience, this newly perceived fraction-of-a-second can be the difference between the “feel” that a web application is usable and on-par with a native application experience.