A. I dont know of any one who has had there facebook 'hacked', only had friends guess/workout/learn other friends pass words, and people saying that there facebook was 'hacked' is one of my pet peeves, I find it really annoying.
B. face book is really good for keeping in touch of friends, and communicating with them, but take it from some one who avoided it for a long time, before eventually joining, It is very easy to get 'addicted' and spend way to much time on it (It is worse then forums for that in my opinion).
C. As for the bullying issue, it is very easy to change your facebook settings to stop people you dont like from communicating to you on it.