Thought parkin': I wonder if anyone within the HCI community in general and the social navigation subfield in particular, has looked closely at mechanisms for group, permission, and capabilities management. I get the sense that Flickr get's a lot of mileage out of a relatively simple system, but I'm trying to envision the extension to socialized aggregators.
Given that you want to expose portions of your reading behavior to different communities what are decent mechanisms for expressing one's intent? Throwaway approach: start with buddylists and go from there.