i don't think the home button should go away.
On a multi touch device, there's always the chance that a user could inadvertently create the specific gesture that would send the user to the homescreen. That could potentially frustrate and confuse users. I can just see it now, you're in the middle of an intense game or something else- all of a sudden - poof there goes your app and there's the home screen.
what about people that lose fingers in oil field accidents and knife fights!!!!! I guess they can't use os4.3~~~