I bought my 2009 Audi S5 in October 2008, after having it order for 10 months from Continental Audi in Naperville, IL (I had originally ordered the 2008 model).  I've taken the car to several high performance driving events at various tracks in the midwest, including Autobahn Country Club and Black Hawk Farms in Illinois with the Audi Car Club Chicagoland Chapter, Putnam Park in Indiana with the for Windy City Chapter of the BMW Car Club of America, and Road America with Badger Bimmers.   For my first two events I ran on the stock Dunlop Maxx Sport GT tires, and prior to the third I decided to invest in a set of Bridgestone RE-11's on 19" rims.  The only issues is that after the third event I had to replace the brake pads.  I did this myself - it's not too difficult, although because of the car's electric parking brake special care must be taken with spreading the caliper pistons on the rears - see here. 

 

In April 2011 I installed the STaSIS/Ohlins SL suspension, consisting of adjustable height coilovers in the front and heavier springs and shock in the rear, plus a beefier rear antiroll bar.  This lowered trhe car about 1 1/2 " in the front and 1" in the back.

 

There is an issue regarding use of the Valentine 1 Radar Detector in cars equipped with side assist - more info here. 

 

Here are the sales brochure, ordering and pricing guides for 2009: