The book looks really good. Congratulations. I know how much work you must have put into it. It would be great if a lot of the arduino knowledge could be collected and written up in this fashion. If the book was quite complete it could be made available as a download and people could get it printed and bound at a printers. It could also be offered as a bound and printed book which people could buy (for and example of this see the Blender open source software www.blender.org, they've released a number of books)
Cheers