Pros: I can make/receive calls.. big plus these days
As a lot of other people have mentioned, all carriers are evil, its just a matter of finding the lesser evil and crossing your fingers.
So far, so good for me. I can make and receive calls (in the Richmond, VA area) which sounds trivial, but apparently Verizon hadn't figured that part out yet. I've yet to have any significant deadspots, even while going to God's country North Carolina for a weeks vacation.
I use an ancient SE z525 with no problems. I had been waiting for iphone 3g to come out, but have yet to take the plunge, so no comments as of yet on the data service/speed in these parts.
Lastly I give ATT high marks for phone selection merely becuase they are a GSM network and you can slamp your sim in any unlocked phone and roll (unlike Verizon).