Where i think Facebook fills a gap is that it creates the feeling that you are in touch with someone without having to go to the effort of phoning/emailing 1:1/physically meeting, in some ways I think there is a guilt mitigation built in there somewhere. When I compare how may parents keep in touch with friends & family through regular calls and meeting I think we have definitely lost something personally and as a society. How much more personal is a one on one conversation can be compared to a facebook post. I always thought there was room for a network that would require a physical meeting occasionally.