I regret to inform you both that my spouse, charming as he is in other ways, does sort books partially by size and so it is in our household: we have shelves that hold paperback-size, shelves that hold trade-paperback-size, and shelves that hold larger mostly-hardbacks. Though this is clearly to pack in the maximum number of books possible, and within those shelves nonfic is sorted by content and fic is sorted alphabetically by author.

(The thing that I have never forgiven him for is that he also puts the paperbacks in TRIPLE LAYERS. I ASK YOU. I didn't even KNOW the third layer existed for years! I reluctantly go along with it because, well, otherwise we wouldn't have space for the books. Although at this point we could probably get rid of the third layer and not miss it.)