I think the main stereotype about Cambridge that's true is that it's academically driven. Some colleges may seem quite lenient with the handing-in of work and so on but there are very few places where you can get away with doing absolutely nothing at all. When I visited a friend at another university it felt a lot less stressed work-wise.
I'm sure there are snobby people at Cambridge, but they tend to stick together as far as I can see. I've never had any trouble with them...most of the people I've met at my college have been really down-to-earth. Some kids are rich, some are poor, some are public school, some are state school...it all varies, just like at any other university.
I know Cambridge is unusual in not letting its students take paid work outside college without special permission, but you can work loads during the holidays and there's plenty of other stuff to keep you busy during term-time.
Speaking of Paul Jefferys, I've met him twice...once when I was at one of Körner's maths lectures (which were randomly recommended to me) and once on Rose Crescent when he was coming out of McDonald's...didn't talk to him either time but he seemed perfectly normal. I don't think I'd have even noticed him if I didn't know what he looked like, except that he has a really bulky nose!