Google books is a great concept and I love the idea that the content of these books is available for anyone to browse.
A simple way to add value to Google books would be to allow users to highlight selected portions of the text; and then annotate them and share them with others. This would make the book come "alive" and would add much more value to the online book.
An e-book can be far more than just a digital version on a print book and allowing readers to
" mark up " books and discuss them will create much more traffic on the site ( which I am sure google will be happy to monetise !) and add more value for both authors and readers.