Researchers found that Twitter users don't post more based on how many followers they have/how many people they follow, but based on how many people they actually interact with on a regular basis, a number that isn't strongly correlated with followers/followees. Self-evident to anyone who's been involved in the discussion over whether LJ should really call it a "friends list," I think.
What I'm interested in is this idea they have that it's the people you interact with among your followers/followees (or friends list) who really matter. True, I regularly exchange comments with probably less than 10% of my friends list, but I have people on my flist who regularly post things that make me think, whose posts I look forward to eagerly, and who definitely have an impact on me even though I rarely comment on their entries and they never comment on mine. I suppose the relationship I have with those people isn't strictly social networking, even though we're using a social networking tool to have it.