When you blog, anyone can read it. Really, of course, your audience
is quite limited. People self-select really fast - I certainly don't
stick around a blog I find boring. Over time, clusters of blogs grow
as people link to each other. I find this kind of emergent audience
fascinating, especially because of the way that readers - and writers
- find each other rather than signing up for something or being
brought into something from the start. You might want to have a look
at Mark Bernstein's a-life experiments of how blog clusters grow -
this is with simulated blogs. http://markBernstein.org/alife2.html I
love this stuff.