[btilly]

The problem is that people who might want to follow might want to follow about different topics.

For instance people want to follow him because they are interested in minecraft, or because they are interested in game progamming. The overlap between those groups is not that large.

People might want to follow John Baez because they are interested in his math/physics blog or because they are interested in Project Azimuth. The overlap between those groups is not that large.

People might want to follow Randal Schwartz because of his Perl stuff, or karaoke. The overlap between those groups is not that large.

People might want to follow Matt Cutts because of interest in SEO or exercise. The overlap between those groups is not that large.

All of the above might be comfortable with some personal stuff being public. But people who want to see their personal stuff has a fairly small overlap with what they have.

In short all of the problems that circles try to solve for private stuff exist for content people are willing to have be public. The simple public/following labels don't address the need.