Can't remember exactly when I had my interview, but I couldn't get college acommodation so I stayed at a Bed abnd Breakfast and got a Taxi in, then left as soon as my interviews had finished. So I didn't get a chance to meet any other applicants or undergaduates.
Yes i am from state school, comprehensive infact, but I doubt that Cambridge discriminates in favour of state school applicants as there is no incentive to do so, and places are probably awarded on merit.
As for your friend who got rejected with 10A*s and 5As tough luck really.