Peer-to-peer computer networks have had an interesting history - especially since the rocket ship rise (and then fall) of Napster 1.0
P2P offers a lot of benefits - lower bandwidth requirements by the service/content provider, better redundancy since there isn't a single point of failure in the system and as clients get better and better (ie more storage, more computing power) the benefits will only increase.
After Napster we've seen continued innovation around P2P.
Probably the biggest commercial success story after Napster 1.0 was Skype. Many people don't realize that Skype uses P2P technology.
Then the folks that created Skype came back with another P2P service for video called Joost.
This weekend there was a bunch of favorable and negative reviews on Vudu. Vudu has developed a set top box that will deliver movies over a p2p network. The founder are smart so i will wait to try out the service before rushing to judgement. I just don't know if a separate standalone hardware set top is the best way to go after this market opportunity.
Of course my favorite P2P service is Veoh (disclosure: we are investors in the company).
Veoh offers a flash based streaming video service. But you can also download the Veoh client software which uses P2P technology to deliver full screen, high quality video (user generated, prosumer and professional video) to the PC, Mac, ipod and Sony PSP. And you can program the client software to subscribe to internet videos or even schedule a recording for your home computer from your office computer. It's pretty much like TiVo for internet video.
I think we'll see more cool stuff this year and next as P2P finds itself in new markets like mobile messaging, real time events, live video streaming and gaming.