It's also worth noting that a lot of facebook's initial appeal, especially when compared to Myspace at the time, beyond its aesthetic improvement, was the fact that it seemed to stand for privacy. The status quo, myspace, was a public-only profile. A facebook profile was accessible only to your contacts or to your school. The available options have slowly but continuously drifted away from that simple promise. A lot of the site's initial traction was driven by huge demand for a reasonable set of privacy controls: myspace was useful but creepy. The argument that the web has moved on in the past six years and that the demand for privacy has lessened is perhaps a red herring, though only time, consumer demand, and viable alternatives will tell: there might be more of an opportunity here than people realize.

Overall, I think this is a really interesting question that society is confronting and it will be fun to see how it plays out.

Side note: I think a lot of the tech press and blogosphere miss a lot of the subtleties here because, well, people like Arrington, Scoble et al. weren't in school at the time, making the cautious decision to open an account. This has been a revolution led by young people, who are often surprisingly concerned about their privacy and don't depend or plan on Internet celebrity for their livelihoods. It feels a bit like eternal September except in reverse: as the demographic ages, the basic tenents erode.