The truth is, it's not books that are being hacked, it's reading.
The emotional bandwidth that people have for books has little to do with the medium itself and more to do with the comfort, escape, relaxation, reflection and learning it provides. If we've learned anything from the explosion of social networks and the rise of the prosumer over the last few years, it's that people crave interactivity, community and real-time information and conversations as much as everything above.
Kindle was a good first kick (thanks Ben), but it's just not there yet. Why? Because it's simply a more modern version, a digitization, of the same format.
The real revolution will come when we're no longer bound (pardon the pun) to the format that ink and paper begat. Imagine being able to click on any given passage and make and read comments (by experts and everyone), see historical facts, related news, literary reviews and criticism...in the moment. Right there, in your comfy chair, with your glass of wine, in the moment. (Harry Potter fans would go nuts.) Talk about choose your own adventure.
Participation is the key. Aside from the fact that pretty soon, you won't be able to make money on physical books, the era of one-sided consumption of information is seriously ailing.
Free the medium and you free the community ... wait, you create the community.