I've had a few occasions to deal with them. The nice part is you get a working phone very quickly. And they honor your original warranty with the refurb. If you live close enough to an AT&T service center, you can just walk in and swap it.
The only catch is you have to give them a credit card number in case you don't send the original phone back, but they do even send you a pre-paid shipping label, so there's no money out of pocket.