Ask to see the the book before it's published, or, if possible, the drafts. This way you can make suggestions ("Why didn't you include a paragraph or two about

Ask to see the the book before it's published, or, if possible, the drafts. This way you can make suggestions ("Why didn't you include a paragraph or two about feature X?") and correct mistakes ("this bug was fixed in version 1.3.4" or "this feature is available under the Tools menu"). You might even take the feedback from the authors, improve your software and have the book reflect your updated version if you are fast enough. Just beware the feature creep, as always, and don't try to delay or annoy the guy, he's just doing his job too. This is great marketing for you and the least thing you want is regret the way it was done after it hit the shelves.