For main warranty work, any service center will repair it. With the little things like trim and things like that, you may only get that done at the dealer you bought it from. I was going to go to a competing service center for some work since I wasn't too ecstatic with the work my dealer did on one item, but the other dealer would only give me a loaner had I bought the car there. So I've been sticking with my dealership for the loaner since they offer me same day loaners most of the time.

Cliff's Notes version: Any dealer will do warranty work. Your dealer may offer you perks and leniency as far as what's covered, in hoping you'll buy another car from them.