I asked my junior engineers this question a couple of years ago. I try to always get the perspective of the younger generations since I have to readily accept that age weakens one's grasp on newer trends. The answer I got shocked me a bit, but I've since begun to adopt their outlook.
Their answer? "Why would you ever use books when there are PDFs now?" They all use PDFs on tablets for everything and I've got to admit that keyword searching 2000 page documents is handy, not to mention the environmentally friendly aspect. Couple OCR'd PDFs with an application like Copernic and you're unstoppable. This obviously won't help those going into engineering exams, and it doesn't help those of us old enough to not want to change our ways, but nevertheless it seems to be the way things are going.