The books could be, essentially, the game editor tutorials in book form. (BTW, I am not a fan of the automated tutorials - I can't watch the tutorial and follow along by doing the same thing without pausing the tutorial and switching windows.)
Here is a great example of a book based on GM
The Game Makers Apprentice. I mentioned in another thread that I found this book to be very inspirational, even though it is not about GE. Game making is game making, the tools (GE, GM, Pygame, your own stuff in Ruby or C++, whatever) are just the details.
That book, though, is selling GM specifically - but indirectly.
There are other examples, too.
This one uses Blitz Basic,
Game Programming for TeensThis one uses Torque,
The Game Programmer's Guide to TorqueThese books all demonstrate how to develop games with the chosen technology. (The GM Apprentice is very good, btw.)
A side effect is that the book brings the tool to people who are browsing the "game progamming" section of Amazon.com or the local bookstore, and some will line Makslanes pocket by laying down some cash for GE, too. (And, I'm sure Makslane would like a few more of you guys to pay for a license.

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