I probably shouldn't admit I have a facebook page. Or if I do, say it's for research purposes only.
This is, in fact, a new kind of media, so there's insight to be gained by its use. It has roots in collaboration tools and can be used as such; however, its intended purpose is "digital identity," to put yourself and your social circle online. You can now keep in touch with friends essentially forever, without effort, even if you move half way around the world. That alone is a rather astonishing new development.
Another unique property of social media is that audiences are built along relationship lines, so any message I send out goes to my friends first, then their friends, and so on. Not exactly the evening news. More like gossip on rocket skates.
Then there is the impression management angle, where a good storyline (the news feed, wall, posted items) can make you appear hip, one of the cool kids. For example, you might hide the news feed item about being an NSYNC fan, and move your Sonic Youth playlist to the top (or is Sonic Youth still hip these days?)
Finally, as people add likes and dislikes to their profile, those can be applied in various ways. Big money is betting on targeted advertising, and they're right. The $15 billion valuation of facebook is based on the per-share price Microsoft paid for a less that 2% stake. The revenue model is proven, but that doesn't mean facebook is worth as much as the Ford Motor Co. The impression I get is the facebook guys play hardball when it comes to capital investments, and Microsoft doesn't mind overpaying for early entry to the market.
Nobody really knows what all this will look like. So any wacky idea is as likely to be right as the next. Also, there are still a lot of competitors. There hasn't been a big shakeout yet, meaning it's too early to tell. I recommend checking out Ning (http://www.ning.com/) for those interested in the mechanics of it.
How To Make $500,000 A Month On Facebook (Silicon Valley Webguild)
Don't Just Follow the Latest Media Trends (Advertising Age)