Here's a metaphor for how we'll think of books in fifty years: like candles.
We use candles now to mark special occasions, for a sense of cozy old-school nostalgia, for atmospherics, for decor, and in a pinch for their original use when the power goes out. But most of the time, when you really want to get something done, you flip a light switch.
In the future, physical books will also be used to mark special occasions (they'll be souvenirs) and to decorate your apartment and for atmospherics and nostalgia, and in a pinch when your computer or portable data device is on the fritz. But most of the time, when you're really going to want to get something read, you'll just turn on your Kindle/iPhone/magic-electronic-gizmo.