As in many media tools in technology there are pros and cons.
For a frum girl for example the purpose she would use fb is to socialize.
An organization will use it to broaden the scope of people and increase their influences by using fb. So, the actual idea of facebook is ok.
For the girl (14 yr old) for example she could get caught up in inappropriate relationships/sites etc. that could damage her yiddishkeit.
The Rabbis who use facebook I think are mostly involved in kiruv and use it as an invaluable tool to access multitudes of people….
the two usages serve to very different purposes and can’t be compared. I think for an average person to use facebook is fine as long as they socialize appropriately and stay within Halachic guidelines. For people who are avid facebook addicts it’s hard to stop so you cant say don’t use it at all…Just use it and only contact the people you should….For those of you that don’t use it good for you and there’s no need to start!!!!!