There's an interesting article in the New York Times Books section, "A New Forum (Blogging) Inspires the Old (Books)".
Publishers like bloggers because they get a sense of you, and your approach to your topic immediately. Blogging also gives you a platform:
Several factors make bloggers' books attractive to agents and editors. "Word-of-mouth buzz is much more valuable than paid advertising," Ms. Lee said. "I think if there's a reason people come to your site, there's a built-in audience."
Publishers were always happy to have authors who already have a platform, said Mr. Hornfischer, who also has started contacting other bloggers he enjoys. That built-in blog audience is growing; because the Web has no boundaries, it is international.
So there you go. You're not blogging for amusement, you're working. :-)