In the nextgen-list, a discussion about library cats is currently going on. Gary Roma has compiled a world-wide library cat map and has also shot a documentary called "Puss in books. Adventures of the Library Cat". Also starring: Dewey Readmore Books, the resident cat at Spencer Public Library. Please note that there is also a library cat society.
I'd love to have a cat around me, especially on lonesome library evenings. But an article in San Diego Union Tribune from 2003 shows that feline librarians can also cause troubles: It says, "a former journalist who claims his assistance dog was attacked by a cat that lived at the Escondido Public Library describes his $1.5 million lawsuit against the city as a 'David vs. Goliath' battle"