Today I was looking closer to Gran Turismo 5 movie clip.
I found that they are using two types of shadows of cars. One is from directional light and another is ambient occlusion.
The shadow from the directional light is done by shadow map. Each car seems to hold their own shadow map.
As you can see from the screen shot above, those two types of shadows don't seem to get along well.
An impressive part is reflections on the car's body. The reflection looks very clear and covers body and glasses part very nicely. I guess they are stream in and out pre-baked environment map rather than rendering them at run-time.
I will be very surprised if the environment map is rendered at run-time. One way to figure out is to see whether other cars are reflected on the car's body or not. I couldn't find that kind of situations from the movie clip but I can test it latter.I tried to see aliasing issues but the movie clip did not carry enough details on edges. HDR was covering edge parts smoothly and Depth of Filed made the look smoother. Slightly shaking camera up and down made the scene more realistic.