Shirky: Social Software and the Politics of Groups

Which looks at how
Social Software Encodes Political Bargains
and Identifies that there is little
Testing [of the] Group Experience

But the most interesting (for my mind) is the notion of Bariers:
"What kind of barriers work best?" Most groups have some sort of barrier to group membership, which can be thought of as a membrane separating the group from the rest of the world. Sometimes it is as simple as the energy required to join a mailing list. Sometimes it is as complicated as getting a sponsor within the group, or acquiring a password or key. Sometimes the membrane is binary and at the edge of the group -- you're on the mailing list or not. Sometimes its gradiated and internal, as with user identity and karma on Slashdot. Given the rich history we have with such social membranes, can we draw any general conclusions about their use by analyzing successes (or failures) in existing social software?