I am a big fan of the unbook concept, popularized by Dave Gray among others. I am currently in the process of trying to turn my Inner Chapters audio essays into a book and not surprisingly am using the unbook model since it so closely mirrors the open source software model with which I am already so familiar.
Mike Masnick at Techdirt links to an essay by Mike Shatzkin that explores the idea of a so-called living book, which sounds like an unbook to me, as a means to foil piracy or, to put it more constructively, to give people a reason to buy the book.
I actually really like how Shatzkin suggests that the bigger market authors who stand the most to lose financially from piracy are also in the best position to add a perpetually updated dimension to their works that would help sustain interest from a buying public. I think we are already seeing this from clueful authors, both large and small, who understand viscerally how being a steady source of information, not just in instantly stale print or digital editions of their works, can drive a much more strongly thriving audience and rewarding career, financially and otherwise.