It's worth noting that while this is becoming available in chrome now, the WebRTC APIs that both Chrome and Firefox are working on (and will likely start showing up in the 3-6 month time frame) is also likely to provide p2p message passing support.

There's a group of people beginning work on porting some of the traditional p2p constructs like DHTs into the browser, for those interested: http://joincollage.com/webp2p