BGR says its contacts have told it that Apple is already testing devices without home buttons. Since Apple likes consistency (witness, the side switch issue on the iPad), the "feature" would most likely its way to the iPhone as well, perhaps as early as the next generation of iPads and iPhones coming later this year.
Daring Fireball isn't so sure, and has a pretty common sense argument for his reasoning:
These gestures do mean that you don’t have to use the Home button. But there’s a serious discoverability problem with them. The physical Home button is impossible to miss. That it is the one and only button on the faces of these devices is a big part of why normal people are able to pick them up, start playing with them, and figure out how to get around with no help. How in the world would a normal person figure out or guess that they need to do a “five-finger pinch” to get back to the home screen?The ability to pick up an iPad or iPhone and use it immediately, or at least start playing with it, is one of its great "features." Gruber is correct that this sort of move would seriously impact that ability.
There's another common sense reason for this, although it's a little grim: There are plenty of people who for one reason or another, are simply missing fingers. This doesn't mean it's not a great idea. It just means that, like keyboard shortcuts on Mac and Windows, this type of gesture would be good as an adjunct, not the main way to reach the home screen.
On the other hand, Apple has surprised before. We will see in April (perhaps sooner) and summer, on the next-gen iPad and iPhone. You can see a video on the new gestures below.