Thinking about documents is one area in which paper is still king. I've got two 27" monitors on my desk, but when I want really think about a document I'm reading, I print it out and grab a pen. Reading things on a screen feels like having a straight jacket on. I can't put several pages next to each other. I can't put my finger on a page so I can flip back to it later. Marking anything up is an ordeal of UI getting in the way. Tablets aren't any better. Writing on glass feels wrong and the lack of friction makes it hard to write small text legibly. And their small size compounds the problem of not being able to refer to more than one page at once.