Though Admittedly I Haven't Heard This Theory In a While
Just in case you've been getting the standard gloom & doom libraries-are-dead digitization-will-replace-all-the-books-in-the-world spiel, here's a nice article giving a whole host of reasons (33 to be precise) as to why this will never happen. Tracy, who brought the article to my attention, liked #5. I'm more of a fan of #23.
Thanks to Tracy for the link.