Facebook is good because it allows me to connect to family members or friends I haven't seen in years. It also allows our family to plan events and have everyone check in and know where and what time it's at. I don't see anything wrong with virtual interaction, in fact I think it's a great way for naturally shy people in person to come out of their shell a bit for healthy social conversation and activity.
The only problem I have with Facebook/Twitter etc., is when people get overboard and use it for all social interaction i.e., takes over their lives. In fact, my facebook is a straight up lie, I have a fake name, fake jobs and fake degrees and my profile pictures are always fun things I've photoshopped.