I don't really have people from online on my Facebook, except a very small handful of people. The rest of my friends list is all friends, family, work colleagues and people I went to school with. If anything, it's useful for offline relationships. Some of my family live quite far away, so it's a good way to stay in touch and see what's going on in their lives. It hasn't affected my offline relationships negatively in any way. Everybody on my Facebook either knows me well enough or I don't really care what they think.