Large peer to peer networks can be very difficult to manage, and a solution developed by researchers in Cambridge is to structure the network as a social network. Their inspiration was the way in which information (gossip) travels person to person through a group of people. A large network modeled this way means that each person is only connected to a few other peers, instead of everyone in the network. With networks consisting of thousands of members, structuring a network this way has proven to be much more efficient.

http://news.bbc.co.uk/2/hi/science/nature/1939928.stm