I have to say that it has been the best all round car I have ever owned. Previous cars have included 2 x E46 M3's and a 997 C2S. The only reason that I am selling is that we have a growing family and as I'm 6'8" there is no way that we can even get a baby seat in the back.
The RS4 is phenomenal. Its power, noise, sure footedness and character make it very special. I also found that its discreet looks were a bonus. Whether on B roads or motorway it always finds the right balance between having fun and getting to the destination.
My one modification to the car was a Milltek non valved, non res exhaust fitted about 8 months ago. If any of you are wavering on whether to fit a louder exhaust I would definitely recommend it. It really brings the car alive and amplifies the V8 to glorious levels. Yes the Milltek can drone at 1800 revs but this easily overcome by either changing down or being easy on the throttle. The drone did not bother me at all and I would buy it again in a heartbeat. I have no affiliation to them but APS in Brackley fitted the Milltek and Ed and the guys there are superb - very knowledgeable and helpful. I had the exhaust removed last Wednesday so I had two days of driving without it on - it really felt as if the car was missing something. I sold the Milltek to a member on here so I hope they have as much fun with it as I did.
So what next.... Well I've gone for a Marmite car - an X6 35d to be exact. Its arriving at the end of September. I did drive the new RS6 and it is an amazingly quick car but really lacks that character of the RS4.
So its V8 to straight 6 diesel. I will miss the RS4 but I'm glad I've owned one of the best cars Audi have ever produced.
Thanks for everyones help and suggestions on this great site.
I agree about the Miltek, I sometimes wish I still had mine. 
