Well, I asked this question because that might be what you'll be doing soon with your iOS device. The yet-to-be-released-to-consumers-but-already-released-to-developers iOS4.3 contains multi-touch gestures like the ones shown in the video here. It looks pretty cool, but sort of loses the "simplicity" of the UI, because just pressing the home button to get back is easier than doing a gesture that requires all your fingers on your hand. Plus, you obviously can't do this when your other hand isn't free. So don't expect the next iOS models to not have a home button.
I think iOS4.2 was a bit buggy, so I hope this version of iOS will reduce a lot of them.
P.S. I tried the five-hand gesture on my itouch, but it feels unnatural and clumsy. I'll probably stick to using the home button when I upgrade to 4.3.