FaceBook's only a small part of the average person's social graph, though.
If you look at my FaceBook Wall or SuperPoke or Scrabulous list, it's mostly friends from high school or violin. They predominate because I have no other means of getting in touch with them. The people I hang out with most in person are all Amherst alums in the area; they almost never appear on my FaceBook, because I can talk to them in person. If I do write something to them online, it's through PlanWorld, which is an Amherst-only social network hosted on an Amherst student organization's computers.
There's another group of friends I have: folks from my Harry Potter fandom days. I'm FaceBook-friends with nearly all of them, but there's little activity between us. Instead, I talk to them over AIM. Why put up with the latency of the FaceBook wall when you can communicate instantly?
Then there are former coworkers from work that I stay in touch with. Most of these people don't even have FaceBook accounts, though a couple do. I use e-mail and LinkedIn to keep in touch with them, or I send them an IM and setup a time to get together for lunch.
I think a lot of people that make a big deal about the social graph are Boomers and Gen-Xers that are keen observers of today's "always connected" culture, but aren't really participants. They know that social networking is a huge part of young people's lives, but have no idea just how pervasive it is or how many options people have. The average American teenager now "talks" through phone, text-messaging, FaceBook, MySpace, LiveJournal, e-mail, AIM, and a half-dozen special interest sites. There've been conversations I've had that were half-verbal and half-AIM, carried on through a mix of typing and talking with the other participant sitting 6 feet away. The FaceBook social graph is pretty inaccurate when you consider all the options for back-channel communications.
There's no doubt it's wealth (all information is). Keeping in contact with people is big business (cell phones, Outlook, vacations, dating sites, etc) but there just isn't a way to monetize this wealth. If it was open source or non-profit, it would be around until people got tired of it), but if Facebook doesn't get money in exchange for the wealth they've created (and soon), then that wealth will disappear and social networks in general may be branded as a bad investment. Actually, if that leads to a free and open alternative, that might not be so bad afterall.
It's amusing to see people involved in industry X continue to blog about how industry X is worth more than people give it credit for.