Really nothing aside from normal wear and tear. The car has 186,000 miles on it, with the original engine, and I have replaced shocks, clutch, brakes, cv's and wheel bearings - nothing out of the ordinary. Currently replacing muffler, heater core and the ignition module. When I replaced the clutch at 175,000 miles the mechanic stated that he was confident that it was the original clutch. The car has only left me stranded once in 5 years.
This car has been an excellent car. With 186,000 miles on it the engine is still extremely strong. The parts tend to be a touch more expensive than the VW that I also own but have found that some VW and Audi parts are interchangeable. I would wholeheartedly recommend Audi and its marvelous GT Coupe.