If I walked into your house would I see books neatly shelved or scattered all over your house? Are you a bibliomaniac?
You would see two relatively small bookcases both packed to overflowing. After letting my library get out of control -- you really feel it when you move, and two-thirds of your boxes are books, and they're the heaviest boxes, too -- I've settled on a system that's roughly "one in, one out." So, the books will pile up and spill out from the shelves, and then I know it's time to do a purge. I like the idea of books in motion; I think a book is happiest when it's being passed from one person to another.