Dire warnings about lost privacy, future regret, stranger danger etc, that's what.
But as it turns out, mostly the kids have figured this out already and they aren't really concerned. It's a generation gap thing. The media usually follows the lines about the risks and the potential for anarchy in young people's use of social media sites, but as Emily Nussbaum observes in the New York magazine:
"It’s been a long time since there was a true generation gap, perhaps 50 years—you have to go back to the early years of rock and roll, when old people still talked about “jungle rhythms.” Everything associated with that music and its greasy, shaggy culture felt baffling and divisive, from the crude slang to the dirty thoughts it was rumored to trigger in little girls. That musical divide has all but disappeared. But in the past ten years, a new set of values has sneaked in to take its place, erecting another barrier between young and old. And as it did in the fifties, the older generation has responded with a disgusted, dismissive squawk."Anyone who regularly uses these social media tools quickly becomes aware of the reach and impact they can have by posting their thoughts and observations, photos or videos on Myspace, Youtube or a blog. Your buddy list, or message board, your cluster of blog friends who comment and talk to each other are an audience that can be measured easily. Big or small, you can see it instantly.
Plenty of free tools can let you know who is using your site, when and where they are from. Try Sitemeter, Clicky or StatCounter for starters. Total anonymity is possible, but that's not really what the new generation of social media useage is about. A lot of it is about branded identity: your real one, if you choose, or a creation.
There's still a long way to go with this phenomenon. It's deep seated, it's generational, it's social and economic. It's not going away.