The interface is in danger of becoming rather complicated if you have to have a way of deciding all that. But lj is already close, because there are tags. If you have a robust tagging policy, the only extra functionality needed is to say 'I want my FP to include Dan's posts that are marked "interesting" but not those marked "boring"' or whatever.
Has the advantage that I choose what I want to see, rather than you choosing for me. If I'm in America and I come to Cambridge for a month, I probably want to opt in to your "Cambridge" posts rather than having to have you opt me in.
Re: A way to make posts public, without having them appear on my friends' friendspages
The interface is in danger of becoming rather complicated if you have to have a way of deciding all that. But lj is already close, because there are tags. If you have a robust tagging policy, the only extra functionality needed is to say 'I want my FP to include Dan's posts that are marked "interesting" but not those marked "boring"' or whatever.
Has the advantage that I choose what I want to see, rather than you choosing for me. If I'm in America and I come to Cambridge for a month, I probably want to opt in to your "Cambridge" posts rather than having to have you opt me in.