That Boomers dramatically alter the social networks they adopt should come as no surprise, according to Lee Rainie, director of the Pew Internet & American Life Project, a think tank that studies Americans' online habits. "Boomers are the mainstream of the country now," says Rainie. "When you attract a mainstream audience, you're going to attract a lot more commercial interests. Boomers validate that this is a big market, and that this is a place where commercial interests can make money."

The twin processes of mainstreaming and commercialization mark an end of innocence on a social network, as younger users lose what was once their private playground or--even worse--have to share it with their parents.

"Younger folks don't want their parents there," Rainie says. "But does that mean they'll all flock to different places?"

Not yet, according to data collected by Rainie and his colleagues at the Pew Research Center. Though a few early adopters may jump ship as a social network that was once on the electronic frontier gets swallowed up by digital suburbs, most stick around--at least until a major new network arrives to supplant the old one, as Facebook has done with MySpace.