Joel Spolsky - Library Apps for Macintosh:
"I really want to be able to shelve our books according to their Library of Congress card catalog number. When you do this, books on similar topics tend to wind up near each other on the shelves. This is a very useful feature if you don't know the exact title you're looking for, or if you just want to, for example, browse a bunch of books about Ruby to find one you like.
Somebody has gone to a lot of trouble choosing a card catalog number that put similar books next to each other, and I've always found that open-shelved libraries with books in order according to some reasonable card catalog system are far superior to libraries with books in order according to acquisition date, size, color, IQ, or IDENTITY column."