A new paper from the Stanford Peers group:

In a Peer-To-Peer (P2P) system, autonomous computers pool their resources in order to inexpensively handle tasks that would normally require large costly servers. The scale of these systems, their open nature, and the lack of centralized control pose difficult performance and security challenges. Much research has recently focused on tackling some of these challenges; in this paper, we propose future directions for research in P2P systems, and highlight problems that have not yet been studied in great depth. We focus on two particular aspects of P2P systems search and security and suggest several open and important research problems for the community to address.