beachyhead - really great that you are helping your DS with this. I'm a great believer in setting up FB with your DCs, while they are still young enough to accept your help with it. It is one of the most used sites by young people, so well worth your DS getting his head around it all.
Yes, it is possible for young people to use FB without being bullied, but there are some really important lessons they need to learn as well:
Make sure you have got your privacy settings set properly.
Never friend anyone you don't know.
Never post anything on FB that you wouldn't want your teacher or future employer to see.
Never slag anyone off on it - however tempting it may be.
Be careful about acting like a tit in public, where your friends could take pics & post them of you.
If there is someone you are not keen on being friends with, it is ok to ignore their requests - if your privacy settings are done properly, then they won't be able to see that you are active.
Never think that private messaging is 100% private - in the same way that an email could be forwarded to anyone, so could a private message. Basic rule, never put something in writing that you wouldn't be prepared to have shared publically.
If you are a girl, don't put a whole load of pics up showing your midriff, pouting and generally trying to look like Rihanna - unless you want everyone to think you are trying way too hard to get a boyfriend!!!!
Probably teaching my grandmother to suck eggs here, but that is some of the stuff I have gone through with my two.