Nadia Cristina, Managing Editor of London-based pm magazine, who was gracious enough to agree to an interview when I was over there last fall, just forwarded one of the fruits of that meeting to me, an article I co-authored with Bruce Marcus titled "Blogs—The new community of interests."   The thrust of the article is simple:

"The power of blogs derives from their online essence: available and update-able 24/7, with global reach, they are tailor-made for targeting narrow and usually passionate niche interests.  They rapidly reach an audience of participants that would be completely impractical to reach in the offline world, thereby constituting a collective intelligence of enormous professional value."

A word about the PM Forum itself:  If you're unfamiliar with it, it's a tremendous resource which every serious marketing professional should know about: 

"The PM Forum is a 4,000 strong regionally-based members' association, formed in 1996, dedicated to raising the standards of professional services marketing and to enhancing the credibility of marketers working in professional service firms worldwide."

So enjoy the article, and explore PM Forum.  (Thanks again, Nadia!)