Here are some quick impressions after clearing the Cappuccino and MX-5:
1. I wish there was a way to adjust the gamma.
2. You can change control schemes in the options menu and map accelerate and brake to the shoulder triggers.
3. In game music has to be turned on in the options menu. I always loved the engine samples in the GT series even more than Forza.
4. The control/physics seems improved and more realistic, but, IMHO, still lags behind Forza.
5. Turn off the stability and traction controls.
6. You cannot tune your car beyond tires and above mentioned stability and traction controls. No damping, swaybar, or drivetrain adjustability. It's just not the same GT without being able to fine tune your settings.
Overall, this is a great free demo from Sony. I'm glad they threw the auto enthusiasts and game lovers a bone with this one. I now have to go play with the ITR in Championship White no less.

*Edit: Can remap buttons and turn on music in options.