BL Ochman led me to hackoff.com today, an interactive blog book (referred to as a blook, which is a poor name). The murder mystery story is just starting, and will spread itself across the blog, a wiki, a website and a discussion forum. The storyalso has the potential to go its own way on the interactive wiki.
Great idea; the first chapter is intriguing and the use of multiple ways of presenting data, including the fictional blog comments that all add to the story. Subscribe to the RSS feed to get installments and let the mystery unravel. You could wiat until the book is published in early 2006, but this is more fun and more involving.