My friend O. has four neat bookshelves. Each shelf is devoted to an author or topic that's clear at first sight, mainly because she owns all of these books: they're in their original bindings, rows of New Directions or Palgrave neatly aligned.
On the other hand, I have several indistinguishable shelves of mustard- and clay-colored library bindings. Because I'm cheap, and because I hate buying books I'm not sure I'll need, but then once I have them out of the library, why buy them? Although that then presents a challenge when it comes to note-taking: Word files? Looseleaf paper? Sticky notes? I don't have a consistent method.
How about you? And do you have different policies for "work books" and "fun books"?