One of the biggest threats to a P2P network is a bad node. A bad node — which occurs through either malicious insertion or malfunction — can block/capture/falsify information flow in the network and thereby threaten its very existence.
It seems to me that an efficient peer production project needs to do three things good:
1) generate input, i.e. be attractive to the volunteer peer producers
2) have adequate post-hoc validation and selection mechanisms
3) protect itself from malicious attacks or internal participants, i.e. the bad nodes referred to in the quote by John Robb cited above.
It is this third aspect that is dealt with in an interesting paper.
* New Strategies for Revocation in Ad-Hoc Networks. Tyler Moore, Jolyon Clulow, Shishir Nagaraja, and Ross Anderson. Computer Laboratory, University of Cambridge