Any peer-to-peer publishing system must provide a mechanism for efficiently locating published documents. For censorship resistant systems, it is particularly important that the lookup mechanism be difficult to disable or abuse.
by Alan C. Kay ffrom Apple Computer - "Most ideas come from previous ideas. The sixties, particularly in the ARPA community, gave rise to a host of notions..."
Network Address Translation (NAT) causes well-known difficulties for peer-to-peer (P2P) communication, since the peers involved may not be reachable at any globally valid IP address.