Jon Udell has been working on LibraryLookup and other mechanisms for finding library content on the web. In the meantime, LibraryTechtonics, Library Stuff, and The Shifted Librarian have picked up on it.
Part of it is about OCLC making their records available to search engines. Now both Yahoo! and
Google in the game. So what you do is put your ISBN in the properly formatted URL and you’ll be given links to libraries that hold it: via Google and via Yahoo!.
Of course, you can go elsewhere to play with ISBNs. There’s fun to be had at Amazon, Powell’s, Booksense.com, and AllConsuming.net.