[pndmnm]

The commenting system on Google Reader (despite being neither open or distributed) is the closest I've seen to a system that acts the way I'd like online. I can imagine a distributed version that would operate e.g. with each of us publishing a feed of things we read and commented on, to which friends could subscribe and publish their own comments on... there are some interesting scaling/complexity issues but it's not insoluble. Some combination of FOAF, RSS, and trackbacks conceptually.

I think the bigger problem is that the era of the semantic web/community standards like RSS, etc has largely passed us by. Participation now occurs on unmoderated sites like Twitter/Tumblr/etc, or on moderated community forums (and in a context where there's interesting content but I can't choose who specifically to follow, I prefer moderation).