Musky
Android Expert
Here is a link to engadget about it... doesn't say too much about it though:
Gmail for Android updated, becomes Market app -- Engadget
All I personally notice is this new little bar that allows you to 'star', reply, reply all, or forward more quickly.
Mine installed correctly and fast also, I did use system panel to kill the running Gmail app in the background first though. I too am really liking it. It took the extra step out of the reply process that was in 2.1.