Haven't really had to deal with customer service yet... I have 4 iPhones on the plan and I like the shared data plan, but I knew what I was getting into before I signed up. The way I feel about it is that I actually have coverage now which enables me to actually USE the data plan that I have. With AT&T and Sprint I had so many service interruptions while listening to streaming radio that it was pointless to listen to streaming radio or music. I use a little or 2GB per month, but between my wife and kids and I we use less than 6GB a month, so the shared plan works pretty well for us. The coverage alone will make me put up with whatever customer service issues they have.
Would definitely be tough to give up an unlimited plan though, just because I wanted a new phone...