Kiruba and Codey point to this interview about PR & Blogging. Though the article is meant for large companies with minimum online presence, even small projects can become PR successes using blogs. I've made so many friends on the net by just searching and reading rants/reviews about blogsnob and then commenting on the blogposts.
Also, I think blogging teaches you how to communicate more effectively and cleanly. For instance, we got this email some time ago from an AdSystem customer:
This program doesn't appear to do what we need... Can you please let me know if this program will do what we want and if not, how to get a refund.