Great list, thanks! I'd add:

PR: Declaring expertise, leadership
Blogs: Demonstrating expertise, leadership and engagement

(I see so many self-declared "leading provider of...", "expert this", "expert that" press releases...but with blogs, it's "show me".)

What a perfect explanation of the power of blogs, especially for those stuck in traditional media mindsets. Thanks for making it so easy for others to see the value in what we do, and how it might benefit them, as well.

More great thoughts to help me persuade my peers and clients alike.

Nice to see a list like this from a "let's promote weblogs"-point of view.

Now I'd like to see a similar list, based on a "let's make an honest comparison"-attitude.

@Hmmmm, I agree. The point that would be in favor of PR are not mentioned. Like:

PR: controlled information, therefore minimal chance of unwanted/negative effects
Weblogs: uncontrolled reactions, therefore possibly unwanted/negative effects
PR:

Good list. I still think there's a definite place for the press release--but not, fergoodnessake, those horrid no-news corporate blather annuncements. If you find the real news in it, a press release can be just as exciting as a blog.
As an example, I was once hired to write a press release for a new book on electronic privacy. Instead of the boring, expected "Electronic Privacy Expert Releases New Book," my headline was "It's 10 O'Clock--Do You Know Where Your Credit History Is?
I had fun with it, and so did the client--and, I imagine, the media that received it.
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Copywriter, marketing consultant, and speaker Shel Horowitz is the author of six books and publisher of five websites, five webzines and three ezines. His two most recent, Principled Profit: Marketing That Puts People First and Grassroots Marketing: Getting Noticed in a Noisy World have both won awards. He's currently engaged in a campaign to get 25,000 people to sign--and spread--the Business Ethics Pledge:
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It could be interesting to add a third column for discussion forums. IE:
PR: submit
Blog: publish
Forums: Respond