No, it's not an illusion and it has nothing to do with facebook only relationships (I don't even know what that is). All the people I contact on facebook I have in person relationships with. For well over the past 3 years its primary function has been as an organizational tool for my close group of friends. Few of us update our status or regularly post on there anymore. They live in different cities, states, or countries now. Groups and events make a fantastic way to plan a vacation with friends and has all the interactive features you'd want for that sort of a thing (messages, RSVP, polls, etc) that e-mail simply can't give you, and the fact that facebook is completely ubiquitous among my friends make it really the only choice for the job (although I do suspect this is due to our age range- we are all mostly in our early 30's - I think if we were older or younger this would not be as true).

Until someone makes an organizing tool that can break the network effect facebook has with my friend group, I'll have a facebook account.