One of my pet peeves is the Book vs. eBook argument. It's a loaded question that's erroneous and perpetuating a false assumption that could, in the long run, harm the public image of both formats. It's not about choosing one format over the other. To frame the question Book or eBook is as ridiculous as making the claim that there is a war between Hardcovers and Mass Market Paperbacks. Or Books and Audiobooks. They're different formats, period. On day one, I might purchase an audio book. On day two, an eBook. On day three, a hardcover. The formats are not engaged in a battle royale where the reader is exclusively sticking to one kind of purchase. Or if they are, it does not necessitate them buying the other formats. For example, if I'm the type of person who purchases audio books exclusively (because they're part of the listening experience during the commute), if they suddenly disappear altogether, I won't suddenly be purchasing print books en masse.
What's disconcerting about the Book vs. eBook framework is that it's a lazy solution on the part of publishers and pundits. Instead of asking how both formats can profit, they are instead playing the blame game and attempt to vilify one format over the other.
Cory Doctorow making his novels available free for download is a popular example of how one could go about with the Book-eBook symbiosis: the free eBooks encourage readers to purchase the print book. Having said that, this is just one model and perhaps unsustainable in the future (or as Paul Cornell puts it, "betting against the future"). It currently works right now (or for some authors) because eBooks are just a small percentage of the market, at least compared to print. It's not a paradigm that can be practiced if your eBook sales vastly outnumber your print sales for example. Similarly, while it's not a relationship that can be outright described as parasitism (popularity of print does not diminish the digital books), it's a model that benefits the Book more than the eBook.
There are other innovative models out there but unfortunately, because they're not accomplished by major publishers, or simply within our respective industries/genres, they're overlooked. Evil Hat Productions for example has an interesting pre-order system for retailers: if a customer pre-orders a book at the store, retailers can hand them a PDF (burned to a CD) so that they walk out with something, even when the actual book hasn't been released yet in print. Paizo Publishing, at least with its gaming line, lets consumers buy the Book along with the eBook (a free PDF is thrown in for free if you subscribe to their Pathfinder line). What's great about this model is that while you wait for the delivery of the print book, you immediately have a product which you can peruse. These models complement instead of antagonizing the various formats.
The success of the eBook does not preclude the death of the book (and vice versa). The real innovators in the industry will find ways to make both formats work without being detrimental to the other.