I do write a blog. As tx observed earlier 99.9% of blogs are crap, including mine. Nonetheless I think it has been a worthwhile use of time, and I'll continue doing it for a while. Written communication skills are very important, an "essay" style of blog can exercise those skills whether anyone reads what I write or not.

The discipline of having to write it all down does certainly sharpen ones thoughts, and comments often supply links to other material on the topic. In my case commenters also point out ghastly errors I've made, but thats probably just me.