Chasing Neil and Nefilin,
When I was initially considering the GTI, I took one home for the weekend (I've bought several cars from them) and the only difference between my car I bought and the one I test drove for the weekend was the color.
In the 60 miles I drove on the test driver car...
I reset the gas mileage on my way home from the dealer which was mostly hwy. On the 15 mile hwy drive home, cruising at 70 MPH, I had nearly 33 MPG on the computer (avg) readout. By the time I got home (another 7 miles) in city driving conditions, I had averaged over 28 MPG (no hard starts or hot rodding since the car was still in breakin period). For the entire weekend, I averaged on the computer readout 27 with about a 50/50 mix of city/hwy.
I was impressed, given my previous car which was a 2007 Audi A4 2.0T Avant manual. That car got 23.5-26.5 MPG on average with city/hwy mix, but it was also 350 lbs more. I could consistently get high 20s and low 30s on the hwy.
On my way home from the same dealer with my new GTI, I reset the computer and checked the avg MPG when I drove. After the hwy stint of 15 miles I had only avg 28.X MPG and by the time I got home the avg dropped to 26.X - again without aggressive driving. I knew right away that there was a difference between my car and the test driver. That was worse than my Avant and I thought it might improve, but it has not for 6000 miles I've driven.
I've taken my GTI to the dealer to have the car checked (90 day insp and 5k oil change), and they said it is normal - go figure.