I got mine just after Apple dropped the price and I am VERY happy with it. It is probably the only gadget I've ever owned with which I am more pleased six months later then when I first bought it. My wife's cell phone is on Verizon, and I get consistently better phone coverage then she does, and the iPhone even worked in Europe as is (no additional service charge, but reasonable roaming rate for telephone. International data service is, however, very expensive) I have all my contacts, calendar for years back and forward, a thousand pictures, and three movies (stuff I was involved in and sometimes want to show people) on it, and have still only used a third of it's memory. The mapping function (including the pseudo-gps location finding by triangulation from cell phone towers), weather, and stocks work fine even on AT&T, and the 2 megapixel camera is an adequate back-up camera in good light (MUCH better than that on my wife's phone). My only complaint is the sluggish internet speed (as mentioned by others), but since I don't use it for email or long internet sessions but rather for quickly getting directions or info on something particular, this is a minor complaint for me.
If you know that Apple is switching to the faster AT&T net work within a few months, I'd wait. If it is going to be a year or more, I'd buy now.