All this talk about hybrid cars.... ick.
To offset that, Sue and I just came back from a two-day, 750 mile road trip in the Vette. Spent entirely on winding mountain roads including the Unaweep-Tabeguache Scenic Byway, which is considered by many to be the best drivers road in Colorado. Excellent surface, amazing scenery, virtually no other traffic and perfect for spirited driving.
Despite spending a lot of time playing around in the twisties and my somewhat casual relationship with posted speed limits, I got 23.5MPG average. For an 850 HP car, I think that's pretty economy-carish.
The only negative was the first day. When we topped Hoosier Pass it started snowing. It wasn't sticking, but the roads were wet from there to Vail Pass.