has anyone considered adding a series of color bands to the labels for coarse/medium/fine grained placement information? For example "coarse" is nonfiction, "medium" is travel, and "fine" is Bermuda, or whatever. If you see a book with a red label in the blue section, or whatever, you know it's misplaced.
If the labels are placed on the book at a similar location, then any book that is out of its proper would be significantly more obvious without having to resort to reading the label of every single book.
Of course the techie solution would be to barcode every book and then have a robot on each shelf that scans the barcodes after hours...