I actually don't mind AT&T. Are they overpriced, yes. Do I get more dropped calls, sometimes. But, anytime I've called AT&T they've met my expectations and I've had two instances were I messed up on my bill and got a ton of overages, which they greatly reduced or waived. Also, I've traveled in Europe and having my iPhone available to make calls was amazing. I'm sure with all the iPhone uses sending MMS on Friday there will be some problems, but they will get it sorted out and things will go on.
All that being said, I would love it if the iPhone came to Verizon, but I'd stay with AT&T for the time being. I just want more competition and choice, it keeps prices down.