Just returned from Bowling Green after 1550 total miles. My 06 A6 coupe averaged just over 29 MPG on the highway - including gas stops, lunch stops, and overnights stops.
In town (my car is my daily driver), it gets just over 20 MPG here in OKC,OK area.
BTW, back in April, the wife and I did the Big Bend Open Road Run in the 110MPH class and the car averaged right at 20 MPG at 100 average for my wife while I managed to get just slightly over 22 at the same average speed.
I drove to Atlanta and back to Northern Illinois and averaged 28.8 MPG on the whole trip including the in town driving and stops. I think at a steady 70mph I was showing 32 mpg on flat roads. I have the 2005 with A4 trans.