There are rumors floating around that the iPad 2 and future iPhones will lack a 'home' button. Instead you would have to use gestures to do the things that currently are supported by the home button.
I think this is clearly a move in the wrong direction. Apple has come up with many smart usability innovations, but its obsession with 'the fewer buttons, the better' is not one of them. Since the very first Mac in 1984, Apple's computers sported one-button mice. Unix devices of the time, and later Windows devices all had mice with more than one button, and for the most part users found this quite straightforward to deal with.
An interface with too many buttons will clearly be more complex. But reducing to zero also adds complexity. Without a home button, users will have to memorize gestures. How to get back to the home scren will not be 'discoverable'. Also it will be increase difficulty when trying to use a device without looking at it, or with gloved hands.
As I said in my earlier post, I think that a three-button device would be better.
Let's home the rumour of zero buttons turns out to be false.