Reddit, Twitter etc. are quite okay for naturally-ephemeral content but if you want to share a stable/growing bookmarks collection, or even cooperate with others sharing their own, there's nowhere to do it. DMOZ used to work quite well aside from the usual controversies relating to its centralized moderation, and a federated variety of that plus something like delicious/stumbleupon for "tags" and folksonomy would be interesting to experiment with.