I recently went to the Boston Public Library to get a specific book that was supposed to be on the shelf. I couldn't find it so a librarian put in a request to have it found and held for me. She noticed that it had been checked out 6 times in the last year, which she said was a lot, and therefore if it couldn't be found they'd make sure to order another copy. (It was http://beinggeek.com/, and it eventually turned up.)