So that's where he went.
Some of the most intelligent, readable, downright smart articles about social software on the internet are written by Clay Shirky. The way that people use and abuse software to create communities of common interest on the internet is completely fascinating; even before Facebook, chatrooms, and their ilk entered public vocabulary, email, usenet, and forum software were fostering weird and wonderful hives of social activity.
Some of Clay's articles are classics. If you ever got into a slanging match (giving or receiving) in an online environment then you should read A Group is its Own Worst Enemy to get an understanding of why this and other frustrating situations are so common.
The other articles available from Clay's site are similarly compelling, so I can heartily recommend browsing through them. Unfortunately the flow of online articles dried up a while ago, and I stopped tracking his site for updates after a year or so.
But hurrah! I've just discovered that he's written a book, Here Comes Everybody: The Power of Organizing Without Organizations on similar subjects. Here is a review from Reason magazine and the book blog.