Paul Graham wrote an interesting essay about public relations firms and the media that also talks about weblogs as against print news: The Submarine. He gives an excellent example of an important difference:

Imagine how incongruous the New York Times article about suits would sound if you read it in a blog: The urge to look corporate-- sleek, commanding, prudent, yet with just a touch of hubris on your well-cut sleeve-- is an unexpected development in a time of business disgrace.

In the essay he describes the PR genesis of a bunch of stories that regularly announce the recrudescence of the business suit, as if these stories were actual news rather than a marketing campaign. He also makes a little prediction:

PR people fear bloggers for the same reason readers like them. And that means there may be a struggle ahead. As this new kind of writing draws readers away from traditional media, we should be prepared for whatever PR mutates into to compensate. When I think how hard PR firms work to score press hits in the traditional media, I can't imagine they'll work any less hard to feed stories to bloggers, if they can figure out how.

I think we've just been watching the conflict get underway with the attacks on Dail Kos.

There are some links here and here.