I figured I start a post here since I haven't heard mention of this book here yet. I found this at the bookstore at Downtown Disney last Friday and had to pick it up. It's an excellent companion piece to the Haunted Mansion book as it's by the same auther, has the same sort of layout, and follows the same narrative pattern as the first one. The first section of the book is dedicated to the creation of the ride, the second section is a detailed walkthrough of the various versions, and the third deals with the creation of the first movie. It hints at changes to be made to the attraction to better suit the upcoming movies, too.
Here's the Amazon.com page on it.