I use Sage to manage the RSS feeds I like to track. I track my friends del.icio.us links RSS feed. When you add a URL to del.icio.us you get to leave a comment on it, like a note. This note comes up with the link in Sage. What I’d like to do is reply to this comment. Comments on del.icio.us bookmarks. Could be in interesting idea.
I heard about a technology that lets you leave notes on URLs for you friends. A Firefox extension could be developed to get all the comments that have been left for your current URL.
Also would be handy is if del.icio.us let you bookmark RSS feeds and then acted as an aggregator for you. I guess this would be pretty server intensive, like a universal cache for all the webs feeds worth bookmarking. People could then leave comments on all the articles coming though. It would be like a web on top of the web: MetaWeb!