There exists a current of thought upholding the idea that the best book is still one that is printed on paper (see the back page of the Book Review a few weeks ago for an example). When I forget that I work in a library and have immediate, easy access to most of the printed books I want, I tend to agree. It's during my forays away from the library that I realize why some of the features of e-books are so attractive. And while I'm not ready to abandon printed books entirely, I can see how a hybrid model might be ideal.
The concept of a book is largely irrelevant to networked
devices, and one big reason that book-related words (page, library) are making the transition to the online world is because books are easy to use. (This is in addition to the reason that books have so far been a common frame of reference.) Taken a step further, e-books exist because printed books are so easy to use.
A hybrid book has the potential to be best of both worlds, in that it could exist both as a physical object and an online object. Most media are being forced to choose between one or the other type of existence, but I think books are fundamentally different and may not have to make that reckoning. Yes, the internet makes it unnecessary to print something out in order to interact with it. But at times, a printed version of a book -- not reliant on a power source or a network connection -- is the most desirable thing to have, no matter how smart your phone is. (Or maybe I'm crazy. After all, I'm still buying CDs because I can digitize them and also have a nicely packaged version to put on my shelf. When I purchase digital music, I'm irritated that I don't get the object. Unless I make the effort of burning it to a blank CD. Which I don't, and which wouldn't be the same anyway.)
So, is anyone selling a printed book with an access key that provides a digital copy for the consumer's preferred reading platform? Are textbooks doing this? Would the book-buying public be willing to pay slightly more to have both formats? I think a similar feature is available on certain Blu-Ray DVDs, but from my cursory reading this effort is meant to prod consumers toward the digital version rather than to support use of the disc.