I wonder if changes to Facebook’s default privacy settings might be relevant here too. Seems to me that more content is now public thanks to those changes, and therefore discoverable by search.

Your contrast between communities and networks is interesting too. Til now, it seems to me, users on social nets have discovered content through people. I add a friend, so I see their content. Communities work the opposite way — users discover people via content. I search for topics, and I discover the people writing about those topics. Changes on Facebook seem to me less a testament to the importance of search on social nets but rather a significant shift in the way those networks are used.

A related thought: Social nets are (largely) real-name, and communities are (largely) pseudonymous. Real-names networks have traditionally been hindered by concerns around privacy. Facebook’s success was a surprise in that respect, although the default privacy settings, which made your content available to friends only, clearly tempered those concerns. Facebooks’s evolution to a more content-centric network — if this is what the new search suggests — is a bet that users will grow more comfortable over time with sharing their content with the larger public rather than just their friends.

I haven’t seen stats on how many people have accepted the new default settings, but I’d be curious …