I think there are two different issues: 1) sharing sensitive information with the wrong people, and 2) sharing types of information with people who don't care to read it

I think the first issue is solved by defaulting to a smaller circle, like Path or like I would expect Google Circles to have. Most of the people I know who use Facebook intend 80-95% of their updates to the same circle of friends, and would only do a full broadcast when asking for information or promoting themselves.

For the second problem of people receiving your more mundane messages as unwanted, tools should provide more advanced relevancy or even manual filters on the receiving end.

I think anything more complex than these solutions is overkill.