We have a spare bedroom at the new place that has been made into the library/office. I've organized the books by the color of their spine. Some people think this is nonsense, but it actually really works for me. When I'm looking for a given book, I have a much easier time remembering its appearance, than, say, the author's last name. Also, it's gorgeous. I did it at my last place, too. The exciting new changes are that I've done it in ROY G BIV fashion (after black and white), and there are no shelves with work stuff or photo albums intermixed - only books, books, books.