I've only been to McKenna and New Century BMW in the LA area. McKenna screwed me over when I took my car in for 15Kmile oil service, but this past wknd when I took my car in, they fixed my sunroof(it came off track) and replaced my MAF sensor no questions asked. So it was a slightly more positive experience.
As for New Century, they were really nice to me even though I didn't buy my car there. However, it'd be even better if they offer to give me a loaner for the day. Although, they don't seem to be too mod friendly, IMO. They were asking about my DAE's, and my UUC swaybars.