From the Google Print FAQ:
Pages displaying your content have print, cut, copy, and save functionality disabled in order to protect your content.
Cut and copy obviously aren’t relevant, because there is no text, only an image.
You can invoke the Print function, but the book page image doesn’t come out because it is a CSS background. In Firefox, you can turn on printing of background images and colours in Page Setup, but it still doesn’t work, because the <div> with the image also has a background-color of white. Someone’s thought of that one :-) Presumably changing the Firefox print code to prioritise background images over background colours would make it possible to print the pages.
Save Page, choosing “Web Page, complete” actually does work in Firefox – you get all the images, including CSS background ones, and the copy of the page is perfect.
The Google Print FAQ also says:
In addition, you can choose how much of your book users will be able to view over a 30 day period, from 20% of your content up to 100%
This must be using cookies. They can’t be doing it by IP address – proxies and so on make that unworkable. The only Google Print cookie I have is a session cookie, although I have a couple of google.com-wide ones which expire a very long time from now. They could be using either of those. Still, clearing cookies would get around the restriction. I don’t know if they’d prevent access if you had cookies disabled…