It's not for everyone, but there are people with a certain naturally social personality for whom it works very well. I went to a high school with 1200 students, but because I was in band and a number of classes that spanned grades, I knew probably 1/4 of the student body personally, and have 100 of them on my Facebook. Apparently it's not the norm, but I had a hell of a good time in high school, seeing these people every day, playing music, learning stuff, and smoking out behind the fieldhouse at lunch time.
My point is that via Facebook, I'm still hanging out with these people. We shoot the shit about current events, and reminisce about old times. With all the pictures, I know what they look like, so it's not hard to imagine the conversations being almost face-to-face. It's like a discussion board of all people I've met and known in real life, and sometimes there's real depth of conversation. It's whatever you make of it.