There are still a lot of books that don't have electronic editions (and that may never have any). I also have shelves full of books that I have trouble letting go, many of which are OOP.
Actually, in many ways I prefer paper books over e-books, but I'm in a phase (probably midlife crisis) where I resent a lot of the clutter in my life, both the figurative and literal kind, so having thousands of books on a tiny memory card is quite appealing. Perhaps some day I'll snap out of that mood where I'd love to be able to fit my entire possessions into a bag.