> I genuinely don’t understand why Google got it right with Circles
Do you mean on google plus? (Or did that feature make it to other parts of the gooverse?)
The feature on Plus that I desperately wanted was "squares", or facets of your online presence that people could individually subscribe to. Just for instance, if Noam Chomsky had been an active poster on all kinds of topics on Plus, I would not subscribe to his updates because I only care about his work in linguistics, not any of his political activism.
But, the way all the current social properties are set up, the poster either has to have multiple accounts and log in / log out or keep separate browser profiles etc, or just posts everything under one account.
It could be better. It could be pretty seamless: allow the author to tag the post with a click or two just before posting, encourage them to tag posts that aren't tagged before posting, learn what tags they use most and analyze the content of each post to prominently feature in the UI the tags that look like they apply. Allow subscribers to subscribe to author+tag pairs instead of just authors. Done.