Yes, T-Mobile has pretty poor customer service. Some of the CS reps are morons with not clue. Other than that though, I haven't had any problems, and actually a couple of times I've dealt with Customer Service were my fault. First I was screwing around with my security settings and locked up my SIM card (the rep. didn't know what I had to do first before entering the unlock code), then when I was getting Worldclass internationl roaming activated (first time the rep had a computer error, second time I never received my confirmation call, but did get some bonus minutes for my trouble, and an e-mail to them verified it was added).
The coverage areas seem to be getting better, but that also depends on the region.