I promised myself I wouldn't add fuel to the fire, but members of the DPreview forums have seen a 5D Mark II Field Guide listed on Amazon. The book has a release date of November 10, 2008 and a price of $20. The author and publisher are the same as the ones for the 5D Mark I field guide, which you can buy now online or in a bookstore or camera shop.
The Photokina Fair is scheduled for the third week of September 2008, and it may be a logical venue for an official release for the Canon 5D Mark II...while the release date for the book is November 10.
I've taken a partial capture of the Amazon screen (above) just in case it's taken down.
Via Imaging Insider/1001 Noisy Cameras