The next big social network -- the one that turns Facebook into MySpace 2.0 -- will be one that lets users maintain not just multiple 'circles' but multiple identities. I don't just want to separate what my parents see from what my coworkers see, or separate what my (hypothetical) friends from church see from what my (hypothetical) fellow members at the local underground S&M club see. I want to be different people as far as they're all concerned.

This will scale in interesting ways. For one thing, advertisers will actively benefit from this model because it will let them target individual personae.

The notion of keeping the name you were born with and using it forever, everywhere, is the original "single sign-on" paradigm. To the extent single sign-on, single identity is suboptimal in cyberspace, it will eventually be seen as such in real life. The use of real names online already ranges from a useless practice to a hazardous one, depending on how common or how obscure your name is.