The real question is how do you make money out of it.
I met my wife through the internet, but she was a friend of a friend. Ask most couples how they met and a lot will say they were introduced by a friend. How do I say it? Well I was introduced by a friend!
Social Networking allows people to spend less time talking to people and still feel somewhat connected. There's no use in it except staving off the loss of a friend. I cut all my friends when I left high school, I moved country and I live in Canada. I don't miss a single friend from back in England, 99% of them were people who I'd have on a facebook account and completely avoid talking to.
The way to make social networking sites profitable, is to make people use them frequently enough without draining resources. Google makes a lot of money, because the data use by a single user is tiny. The data use by a Facebook user is huge, my wife probably uses 10 megs of bandwidth every time she checks the site. Yet everytime she hits google, she probably uses 10k of bandwidth from a google server to get where she wants to go.