I can maybe see folks outside the US where there are several providers on which to use the iPhone buying one without a contract.
But in the US? What good is the phone without Data? You need to have the service ATT provides (as crappy as it is) in order to fully use the phone so whats the upside other then really wanting one and not being eligible for upgrade.
Don't get me wrong, I'm not one to tell people how to spend his or her money and god knows I'm not very smart when it comes to spending my own, but even I had to take pause when the 3GS came out and I wasn't able to upgrade.