According to Chris Davies of Slashgear.com in his article "Nikon D400 imminent? Guide book coming in July"  a screenshot of the German version of Amazon.com revealed a pre-release of a Nikon D400 Guidebook in hardcover to be released sometime in July.

The supposed author Michael Gradias adds some credibility to this rumor, but I found myself scheptical.  I decided to do some release on the author and found a list of all the books he’s written here.  No mention of the D400 anywhere.  Big surprise there, but I like to be thorough so I did some more poking around.  Though neither Amazon.com nor Amazon.de currently list any books on the Nikon D400, its possible they had just removed the slip.  I therefore went to Michael Gradias’ site and did some searching.  No mention of the D400.

The next step though provided a little better results.  I did a search on the ISBN number listed in the Amazon.de screenshot and came up with DealOz.com.  Now it looks somewhat promising just by the fact that it is listed in Mr Gradias’ results for books he’s authored, but I wouldn’t classify it as conclusive by any means.  I’m not convinced its a reliable site.  I did a manual ISBN search through about 10 other book sites and all came up empty.  I’m going to label this a probable hoax, but I suppose it is a plausible rumor.