Some of the change is cultural. Users have been flocking to social networking sites like Facebook and Twitter, where they voluntarily share all kinds of details about their lives.

In some ways, the meteoric success of these sites could be a reaction to anonymous blogs and public comment boards, which can often devolve into name-calling and polemics. (A famous Internet axiom called Godwin's Law holds that the longer an online discussion continues, the higher the odds that someone one will compare somebody else to a Nazi.)

"The nasty anonymous world is certainly still there, but I think people are trying to create protected spaces where they are a little more insulated from that," says Mary Madden, a senior research specialist at the Pew Internet and American Life Project. "It is becoming increasingly difficult to think about being completely anonymous."

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