Like so many other users, I love my new 3GS iphone. I had to leave Verizon of course to switch over and it's the one thing I regret. I live in the Bay Area of California and I would expect ATT to have excellent coverage there. But noooo. There are alot of dead pockets including in my home (yet the ATT coverage map indicates I'm in a very good zone). In addition, while standing still, the signal strength bands on my phone can fluxuate from nothing to several and from 3G and E networks. Not so stable in my book. Finally, when I do access the 3G network, sometimes it's horribly slow to the point of being worthless. I am hoping Apple is taking serious note of these issues and realizing it is significantly effecting their customer satisfaction.
On a more positive note, there are of course times (about 60% of the time) when things are working well with the ATT network, and then I have no complaints. Also when I've called ATT, I've experienced very good customer service; something I consistantly encountered with Verizon.