This sounds like a scam to me.
You are basically asking people to give you BTC, trusting that you will actually hold a drawing to give people .1 BTC as part of the contest.
I am also missing the point here. Why do you need 10 Bitcoins to make it public domain. Is that a theoretical figure you placed, on what you would have earned, if you sold the book?
Rather put the book out there and try to sell it or get donations, the last option, being your last resort or is this already your last resort?
Well anyways, I will consider it, but I do not promise to do it.. Let's see how it goes.

I've worked a lot to make this book because I think cryptography is very important but GnuPG (like most free software projects) lacks decent documentation, so I decided to write a guide to help others. My point is: I want to make money with the book
AND help the free software community, so to balance things out while I don't raise 10 bitcoins the book is available under a restrictive sharing license (Creative Commons BY-NC-ND), anyone can share it but I hold the copyright. After I raise 10 bitcoins I will release it to the public domain, this way anyone can own it and do whatever they want with it. To "accelerate" things I am holding a contest and giving 10% of my profits to the participants, thus the contest.