I try to maintain a small RPG book collection of books I really like that I want to know in depts. Thus I frequently pass books on that dissapoint me, adventures I've run that I do not intend to run again etc. Thus there is about a meter of actively used RPG books and a pile of 5-6 of books I am in the process of passing on. There is a good german word for this approach: wissenschaftlicher Handapparat [research on-hand magazine]
As someone who went to library school (though I've been working in software for the last couple of decades), I'm ashamed to admit most of our books aren't organized at all except in broad categories. We've got a lot of bookshelves and a lot of books and not enough time.