for game demos, definitely! It is not a p2p network, per say, but an upload while you download way of getting files. Instead of the server sending out 10,000 copies of a demo, it sends out small pieces of the demo to loads of different people, who, in turn, send them out to eachother...distributing the file to many people at once while dramatically decreasing the amount of copies of the file the server has to send out. It instead just acts as a traffic cop, telling who to send what pieces to who.
introduction
it only runs while you download a file and keep the window open, no spyware, etc.