My company Kontiki (http://www.kontiki.com) has been providing peer-to-peer solutions for a while now. We do require a client installation but that's not an issue in an enterprise environment (our target market) where central software distribution is the norm. Most importantly, an installed client allows us to overcome the HTML5 Web Storage limit of 5-10MB. You can't really store much video content with that limit in place.
Peerkit's caching layer hacks around the HTML5 localStorage limit by opening iFrames to multiple top-level domains. Agreed that it's a messy solution that introduces some overhead (loading iFrames), but it seems to work.
