I drive an A6. No real problems with it other than, for awhile, the engine check light was on for no reason. Ended up bringing it to a mechanic to turn the light off since they wouldn't let me pass the smog check test with the light on. It was the strangest thing.
Other than that, I love it. Quattro is awesome, interior is gorgeous, and you have a much better connection with the road than a Lexus or Mercedes. I bought mine used and it came fully loaded--going from a standard Toyota sound system to a full Bose setup was joygasmic.
Honestly, Audis, BMWs, and Mercedes all have maintainence issues--none of the German luxury makers are that great in that regard. If you want a very low maintainence luxury car, get yourself a Lexus IS300. If you want a driver's car, get an Audi or a BMW, you can't go wrong with either. I personally think the Audi interior and exterior look much better than the BMW (and most car magazines agree), and while the BMWs have better engines, Quattro sealed the deal for me. The thing has a death-grip on the road. I do not like Mercedes. They handle stiffly and you feel very insulated from the road (especially in the S-classes). They are nice passenger cars, but you can get a better driver's car.
That's a great deal. Assuming that the seller isn't selling you a song, I'd be all over that like Michael Jackson on Haley Joel Osment.