The Google Car Interior
David Silver

I would say seat belts are still important for safety reasons, even though the car wouldn’t crash into something, it is likely someone can crash into you and there is very little the self driving car could do about it, at least unless all cars are aware of each other.

Also facing forward will cause less dizziness due to movement, some people experience some motion sickness when moving backwards and looking through the window. Maybe seats than can turn around would be an interesting concept. Those are my guesses though.