She said that there is little overlap between the populations of the two Web sites and asked members of the audience to raise their hand if they had an active Facebook page and then to raise their hand if they had an active MySpace page. Almost the entire audience had a Facebook page but not a MySpace page.

She said that in her work, she interviews teenagers across the U.S. and has been asking them which service they use. She said that they go to the site that's where their friends are. She said that teens see Facebook as a safer site and also as a site that's where old people and adults are.

"Facebook users condescend to MySpace users but not vice versa," she said.

She argued that the shift from MySpace to Facebook is "the modern incarnation of white flight to the suburbs" and that this theory is proven by press coverage, which depicts MySpace as seamy and Facebook as safe.

"The kids on MySpace are the riffraff white people cross the street to avoid," she said.

She said that fear of MySpace is similar to fears about the urban. She said that people fear sexuality.

She said that the division between Facebook and MySpace may have to do with their origins, with the fact that schools are not truly integrated, and that these are problems that really matter.

Facebook, she noted, started out as an ivy league Web site while MySpace is connected to the music business. Some of the kids she interviewed said that the "honors kids" were on Facebook while the wanabee white gangstas were on MySpace and that the Hispanic kids "who could really fit into any group" had their own space.

She added that teens are almost entirely absent from Twitter.

"There is persistent inequality," she said. "We find it difficult to talk about these issues. We rely on awkward British terms to describe class. There is no universal public. There is pervasive stratification online."

Referring to recent events, perhaps to the election of Barack Obama, she said, "we must not confuse an advance with the solution."