For every person who's had a bad experience with a company, there's two more who think it's fine. I started out with Cingular and have stuck with AT&T ever since. Yes I've had my ups-and-downs with them, but for the most part have been pretty happy with my service. The iPhone doesn't get as good reception as other phones I've had, but I hardly blame AT&T for that. And when I call their customer service numbers 99% of the time the people are extremely pleasant and helpful, especially their tech support.
So I have no issues with the iPad working with AT&T and I would happily buy it from an AT&T store if I didn't have immediate gratification issues and want it shipped to my house day one.