I now have every car in the game, thanks to the GT Planet forums. A bit of cheating, but I think at this point it's okay to do. I had 2 races left in the S-Class races before I beat the game, and didn't feel like running 1000 races back to back to get that F1 car.
Speaking of the F1 car, holy shit. Wow. Makes everything else seem like a Fiat Panda. I was flying past other Ferrari's, GT Tuned Corvettes, Vipers, etc. All the fast cars in the game just seemed dull after driving the Ferrari F1 2007. Especially with the cockpit view, it just adds to the sense of speed.