The effectiveness of reputation systems for peer-to-peer resource-sharing networks is largely dependent on the reliability of the identities used by peers in the network. Much debate has centered around how closely one?s pseudoidentity in the network should be tied to their real-world identity, and how that identity is protected from malicious spoofing. In this paper we investigate the cost in efficiency of two solutions to the identity problem for peer-to-peer reputation systems. Our results show that, using some simple mechanisms, reputation systems can provide a factor of 4 to 20 improvement in performance over no reputation system, depending on the identity model used.