According to Danah Boyd, a fellow at Harvard University's Berkman Centre for Internet and Society, Facebook presents itself as a quiet community full of upstanding citizens and clean, easily navigated neighbourhoods. Meanwhile, MySpace is the definition of urban blight, with ugly tags and abandoned profiles all over the place.

Boyd borrows the concept of "white flight" from urban sociology to explain his controversial views. For example, for the past few decades, whites have fled Detroit for the suburbs, emptying the urban downtown. The spam is like graffiti, and the abandoned profiles like deserted buildings. In this case, Facebook is cookie-cutter Ann Arbor, and MySpace is wild Detroit.

So why are black people so well represented on Twitter? Perhaps it's not matter of culture but usage, says Joshua Errett of Now Magazine, "it seems clear that a certain black audience gravitates to the more open, free-expression platforms where there are no content rules and the pages are more customizable. Like Twitter and MySpace."