 I purchased my A8 a year ago and have found it to be a very pleasing car to drive. The car was certified and in the 18,000 miles I've driven it, there have been zero problems.  My car came with 19" wheels but I had a set of 18" from a previous car and when the tires on the 19's were worn, I replaced them with the 18" wheels. This resulted in a quieter and more compliant ride with no noticeable degradation of the handling (for my driving style). The A8 pleases me greatly and I plan to keep it for a while as I don't care for the newer "Big Mouth" front design of the '06 on models.  Service is expensive but Audi does sell a prepaid package that is well worth the money. Overall, a great ride.