Interestingly, in all the twitter-rage over AT&T, the lack of MMS and tethering, and the upgrade pricing, I haven't seen very many people who say they're actually not gonna use an iPhone as a result.
I'm definitely having second thoughts. I'm probably not going to upgrade until my contract expires next summer, but when I do, I'll have options. A Palm Pre or one of the forthcoming Android phones plus Verizon will probably be enough to get me off the iPhone.