Llyod Trufelman and Laura Goldberg have a great introduction to blogs in Public Relations Tactics. Just right for those vaguely familiar with blogs. From their article:

The most important thing a publicist can do before pitching a blogger is to carefully read his or her blog. Unlike beat reporters at typical news outlets, bloggers are extremely idiosyncratic in choice of subject matter and slant. In order to begin a conversation with one - and it should be viewed as a conversation, rather than a pitch - it is vital that you are well-acquainted with the interests of the blogger. Many of them still consider their sites to be personal forums for their views and perspectives, and are wary of corporate or PR interference.

In fact, many bloggers have no experience at being pitched by publicists. Recently, we conducted outreach to several blogs on behalf of our client Business 2.0 magazine, which had published an article about the Web log phenomenon (www.business2.com/blog). What was striking throughout the pitching process was the discovery that most bloggers were rarely, if ever, approached by PR professionals. The campaign drove traffic to the story, but it also created a flood of commentary on several blogs - questioning how, or even if, PR pros should get into the mix. Prominent bloggers that joined in the fray included Paul Boutin and Jason Kottke.

Their point about reading the blog first cannot be made too strongly. Reporters are used to receiving press releases and take it as part of their job. Bloggers are not interested in sorting through a vast collection of press releases on the chance of finding something interesting.

However I have to disagree with their strategy for selecting blogs to pitch to:

Another boon for PR pros is that bloggers tend to read other blogs and comment on them. It is not surprising to see a single hit on one key blog turn into mentions on several others. For this reason, it is best to begin your campaign by contacting the most popular, targeted blogs. Most blogs feature sidebars highlighting URLs of other like-minded blogs. Any site that is mentioned several times by other blogs, and that is included in a majority of recommended blog lists, should be noted as a primary target.

The problem with this approach is that everyone else has the same idea. Better to notice which blogs are followed by the most popular bloggers, that is, which blogs do Dan Gillmor, Ed Cone, et al link to? Get your client's story on those blogs and it is likely to be picked up by the larger blogs and ultimately the mainstream press. I think it makes sense to start at the bottom of the media-food-chain, rather than the top.