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It would be pretty bad ass if the entire screen worked as a button (like the trackpad) so you can go home. You tap the screen to select something or click the screen to go home. :-D
Sounds like a good idea to me as it could add another layer of interation to the system. Click corners for setting switches, Expose-like multitasking, Dashboard widgets or returning to the home screen. Click center to standby. Buttonless system, except for the volume ones, but that could be arranged. Swipe screen to the right and volume bar shows up. When the iPhone is in standby, click upper/lower half of screen to raise/reduce volume, without waking up.