I have 2300 miles on my latest Grand Prix, mileage is about 24 on the highway, 16-18 around town or 10 depending on how it's driven. I had a 2002 GTP and the difference is like night and day. This car rocks, and suprises anyone who tries to race it, including factory riceburners.
It's not cheap to own, just check out the price of tires, but I have to say, this is one great car.
The only problem I've had to date is that the front main seal was torn and began leaking @ 100 miles. It took them part of the morning to replace it, otherwise, no other issues.
They built a really fun one this time. Anyone else have anything to add?