The iPad three will probably have a button, but you'll never use it. Before the iPad 2 was announced there were rumors that Apple were preparing an iPad without a home button. There was much debate and the rumor seemed drastic. But the rumors are actually true. [youtube a52zu-ocAd0]
New interface gestures for iOS 4.3 which shipped on the iPad2 lets you multitask without using the home button. Pinch to homescreen let's you close apps without the button and swipe up to reveal the multitasking bar let's you exit apps that are running in the background. Effectively making the home button a relic of the past.
So from the release of iOS5 (probably with the iPhone 5 this june) you might never need to use a button on an iOS device again. Some of you might think that's a great thing, I for one would love it since I rarely double click fast enough, and others might think it's useless.
The tail end of this effect is that you could, theoretically, controll all the interactions with apps running on an Apple TV with a Magic Trackpad...
Let the rumor mills run wild! ;)