The mechanism that I would suggest is to have what I'd call "public circles". These are circles that I have, that I can talk to, that anyone can join/leave. That way I can easily separate out content by type (eg technical, jokes, kid stories, etc), and not worry that pushing things out is drowning people in unwanted types of content.
You might say that I can just add people to circles that I manage. This is true, but it requires me to know who wants that content, and requires people who want it to know that they can ask me for it. Both are barriers to sharing information that I don't mind being public, but don't want to bore people who know me in different contexts.
You might also say that this is equivalent to a simple form of tagging. This is true, but I think that it would make for a simpler UI.