"In time, though, people may very well decide they are comfortable with their social networking being public by default. That will be a different world, and today will have been one of the most important days in that new world's unfolding."

Isn't that world here already through myspace and xyz social networks? FB's value proposition was that it was a safe place to keep in touch with people in your life. Now it's changing its entire strategy and value proposition because Twitter took one feature and implemented it really well. Is the whole data and search business model that much lucrative to risk the trust and stickiness of its userbase?

In my opinion, I think facebook should improve on its strategy for encouraging real online identities. they already started this with fb connect. I believe there's value in knowing who people really are on the web.

Fb == extension of real life on web. Only makes sense for them to improve that identity platform.