I like it too. I can write multiple emails at once, and a chat box will never be in the way of the composer. Maybe there should be a "snap back into page" button thing, but people seem to forget that there is a pop out button if you want a more mono-tasking email style.

Additionally, with this interface, it could be more integrated with hangouts and cross google's services (maybe easier send email pop up on andriod tablets?).