The one downfall I had with it was, it is hard to know what exactly you are shooting at. That is why GoPro sells the upcharge for the lcd back. The other problem I forsee with using the the LCD backpac underwater is that you would be unable to see it while also using the floaty backdoor.
I also used an aftermarket flat lens to fix the focus issues underwater. GoPro has, since the taking of this video, released an underwater housing, and the new GoPro 3 housings had flat lenses.
My feelings on the GoPro camera are that it is a very good small camera, With alterations it obviosuly makes a good underwater camera.