The Audi TT problem was solved by spoiler and changes to certain angles of the suspension geometry.
At very high speed, drivers in Germany were coming off Autobahn ramps (still at speed) and the car was switching ends (to say the least) due to lift-off oversteer. ie the brakes were on, shifting weight forward, the rear-end came untucked, and on turn-in went loose.
I have a TT with the wing/changes at the moment, and I tried to induce the car to do this when I had it on the CART track on the lakefront in Cleveland. Either they really did fix the problem, or I wasn't trying hard enough/was too scared
-A