On point number 3, I have a thought that I think I mentioned one other time but it didn't generate much discussion. I'll bring it up again just cuz I still sort of think it's a cool idea.
Rather than me tagging my posts as #music.doesntgolf (and as #music), I think it'd make more sense for me to just tag my post as #music, and people who wanted to follow just doesntgolf's music posts can follow #music.doesntgolf. That way it's not so much creating a completely separate tag, but people could still only follow my posts in #music, if they don't want to see the rest.
This could also have the benefit of extending to domains as well. So I could follow all of thenewgreen's posts tagged #thehumancondition in the npr.org domain. Or I could follow all posts from aeon.co with the tag #blah. And so on. It would allow for further user controls over what to follow. And I wouldn't have to tag my posts as both #askhubski and #askhubski@ (I believe that's how it currently works?). I'd love to hear others' opinions on this.
EDIT: to put it more clearly -- we can follow any user, tag, or domain; I think we should also be able to follow any combination of these, rather than only the user/tag combination.