How do you organize your home libraries, nerdfighters?
I own many hundreds of books, all packed into my tiny room. My shelves don't leave much room for creativity, so I cannot use the celebrated 'color-gradient' organizing method. I've opted for a rough category system instead. Librarything.com helped me out a lot!
These are my current categories:
-fantasy / urban fantasy
-'real' literature (classics / modern classics)
-books about books/writing
-YA authors who are friends (John / Maureen / E. Lockhart / Scott Westerfeld / David Levithan, etc.)
Edit, November 2011: Hiya! It's been a while since this post, and since then my home library has changed. I've got fiction, YA, nonfiction, biography + memoir, drama, poetry, reference, and travel. This makes a bit more sense than the last system, I think!
If you're interested, I've got my whole library photographed and catalogued here. Enjoy!