I just started removing the books from my shelves so I could add a new one - which happens to entail moving three of the existing bookcases even if I didn't desperately need to reorganize, so ... down they all come.
I haven't figured out my non-fic classifications yet, but I currently have separate piles for:
Fantasy, Light Fantasy, Urban Fantasy, Science Fiction, Mysteries, Light Mysteries, Historical Mysteries, Anthologies and (general) Fiction.
Will probably add a YA category as I still have a fair number of my "kid" reads.
This is going to take forever, yo. Especially as I'm also seriously considering breaking into the one bookcase I DON'T have to move. I mean, I'm already tearing things apart, might as well go all the way ...