I think @jpbari is right.
When I simplified the privacy settings, it was easiest for me to treat the “Per Activity” setting as basically private. I was already touching a lot of code, so I wanted the initial release to be as simple as possible.
Thinking over the options, it seems to me that Per Activity should be interpreted as “basically public, with some hidden activities”. My logic here is that there is already a Just Me option to be completely private, so if you need some half-step between private and public then it should fall slightly more on the public side.
I just need to work out the implementation, and if there are any edge cases that could surprise people. The first example I can think of is someone set to Per Activity that is intending to hide all the activities in a particular city - if that setting inherently shows the user in all city pages then I’ve surprised them. This doesn’t seem too realistic to me, though, but then again I’ve been surprised by some people’s approach before…
Update: This is fixed now so that the “Per Activity” definition more accurately changes to:
You’ll appear in all lists/leaderboards/etc, but each activity will have its own public/private setting which defaults to the setting in your activity tracking service