They might be on or near a shelf, but are they organized? Nope.
Books I've already read are usually upstairs. Books about architecture are usually in the living room. Books in the 'to be read' pile are in the office. Writing and design books are in my studio in the garage. In my bedroom are 4 glass enclosed cases that are doubled up with fiction. That means you can't see all the books because inside the cases are two rows of books one in front of the other.
I'm a librarian. All fiction should be organized alphabetically. I don't think I would ever recreate the Dewey Decimal system in my house, but I would definitely organize my non-fiction into categories and then alphabitize from there, but I don't.
It frustrates me to no end. I buy duplicate copies of books because I can't find them. I have a number of different cataloging software, but I can't keep up with it. I just buy too many books. I also don't have long linear lengths of uniterrupted wall to organize everything.
What does one do? Weed? Heaven's no! Take over the children's bedrooms? Not yet. Take over the children's playroom? Maybe. Buy more bookcases? Always the best solution.
The Studio
The Bedroom
The Nightstand
Kids Room
Kids Room
Living Room
The Office
The Desk