I've just begun to look at the details of the S5, and plan my custom S5 for European delivery. As a Golden Gate chapter member of the Audi Club, I tend to work with Carlsen Audi in Palo Alto. These folks have a very reputable dealership, are knowledgeable, and are huge supporters of the Audi Club. If you are looking for a dealer to start working with, and are looking for a dealer that will give you their best price, just because you're an ACGG member, then my might want to look at Carlsen. Their website is at http://www.carlsenaudi.com/index.htm?bhcp=1
BTW, I am not in any way affiliated with these folks, but over the years, I have been very impressed with their sponsorship of the club.