In high school ('01-05) I had a site called "rants". It was a blog read by maybe 10 people total, including my parents. I happened to email O'Reilly to ask about something and they noticed the blog in my sig. They invited me to start posting reviews in exchange for free copies. I only got through two books but it was fun! Anyway, I found my old review of Learning Perl on the wayback machine:
2. To promote my book. I hope readers of my blog will be tempted to buy The Geek Atlas.
3. To quote Alain de Botton: "Authors write things down so as to have to think of them less."
4. It helps me practice writing.