William Gibson, who doesn't so much predict the future as interpret it for us ahead of time, says the ideal future for digital books is print-on-demand:
My dream scenario would be that you could go into a bookshop, examine copies of every book in print that they’re able to offer, then for a fee have them produce in a minute or two a beautiful finished copy in a dust jacket that you would pay for and take home. Book making machines exist and they’re remarkably sophisticated. You’d eliminate the waste and you’d get your book -– and it would be a real book. You might even have the option of buying a deluxe edition. You could have it printed with an extra nice binding, low acid paper.
I'm always surprised at how little attention the environment impact of paper production gets in the print vs digital debate. E-readers are better for the environment once you read about 20 books with one, but this always gets overshadowed by arguments over aesthetics, usability, and price. I would have thought that the same people who read lots of books also had the most verdant of green streaks.