Great Blogging Case Study!
UPDATE: They have blocked free access to the study, I guess all of the traffic made them reconsider since they charge for other case studies they have 
The points of interest below still apply, and if you are willing to pay $9 or so this may be of some value to you.
UPDATE #2: This report has been purchased and I have attached the relevant copy as a word document for your view.
How to use a blog to increase your online sales after traditional keyword optimization and other online marketing efforts fail.
Here is the most relevant excerpt:
RESULTS: Site sales tripled during 2003, and have continued strong in 2004. Altogether, blog content helps to bring in about 35% of total site sales — 10% from the email newsletter, 20% from affiliates who often reuse the content, and 5% from Blog traffic itself.
Blog readers are among the traffic most likely to convert to buyers. “Six to eight percent of Blog readers buy something. Once someone finds a Blog entry and reads the whole thing, they are about as qualified as you can get.”
