I have a comment, and I'm prepared for it to not go over well:
I think you should make a serious effort to avoid polarizing language, especially early on in the book. To be clear, I'm not at all looking to argue the truth in calling Microsoft "the arch enemy of free software". I'm saying that before seeing a thorough argument laid out, that sort of language is a huge deterrent for someone very new to all this. Since your book isn't about the free software philosophy itself, what I would recommend is focusing only on the positives of free software and using mostly neutral language when proprietary software needs to be discussed. Give a good amount references on the philosophy and benefits, so they have places to look around for more information. If they're interested they'll surely form their own opinion on the non-free.
I do think it's a good idea, and hopefully it's successful. Release it under a free culture license, and for the printed version you can probably ship it alongside Trisquel 6.0 cds. Good luck!
