Great post! This stuff is all very much on my mind — and, as you’ve found, some of these features (ratings, for instance) already exist in NewsGator’s system. (I’m not the only one at NewsGator thinking about relevance!)

In the meantime, if you haven’t seen the smart lists feature, check it out. It doesn’t do everything possible, but it does do some helpful things. (It’s kind of like smart playlists in iTunes.)