Here's a note I received from Mike Vogel, author of Isn't That Bigamy. For more information about his book, see: http://www.isntthatbigamy.com.
"If you can get one blogger with a readership of 50 to mention your book and another blogger with a readership of 500 links to that story, you just marketed to 550 people. Now, if any of those 550 link to it, you can have exponential growth in awareness."
Within the blogging community, it is common to cite other blogs. If you get mentioned in one blog, there's a good chance other blogs will notice and link to that post. As more blogs post to each other, you reach a larger and larger audience. Zoom. You get noticed.
Blogs might well become one of the key book reviewing and publicity media. Indeed, they have already created many sales for some books, especially the off-beat novel and the unusual nonfiction book that can inspire specific fan intest.