Bought my biturbo S4 wagon in August 99 and loved every single km spent in it since.
First of all, Audi quality is top notch, probably the best among european brands. Material choice, finish, assembly, feel are all above the pickiest criticisms.
Low end torque is simply FABULOUS, turbo lag is perceivable but easy to get used to, but then, there are few cars that can accelerate from sub 1500rpm in 6th with such brute force. The subtle whistling of the blowers is addictive, traction is faultless, dry and wet roads alike. I make an average of 11.5L/100km, but hammering or intensive city driving can get the fuel tag much higher. Seldom push the revs above 4000rpm, there's so much down below that it's absolutely useless.
Handling is quite neutral, mild understeer at the limit, never got any oversteer (except when turning off ESP on snow). Overall, the grip provided by the default 17" wheels is excellent, a good balance betwen efficiency and comfort. The beast is heavy though, brutal driving is not the way to get the most out of it.
Warning: car is heavy, tire wear is highly dependent on pressure, driving with 0.3 bar less than spec'd ruined the front tires in no time. Also experienced some vibrations when braking.
Overall, I did not regret my money a single minute and warmly recommend the car.