a dead tree book? ewwww how gauche!
i bought a book from an indie author that included a code for a free ebook copy. all one had to do was register your email address on his site and the code from the book and he'd send you a copy. i don't know how that would work in retail where people could just rip it off but maybe that could be some type of online retailer/publisher bonus offer. i know b&m book sellers would have a conniption over it but alas.