The online Barnes and Noble store (barnesandnoble.com) uses ISBN-13 in the links to books. (e.g., RESTful Web Services) Amazon.com uses ISBN-10. Something to keep in mind to et LibraryLookup to work for Barnes and Noble.

Jon Udell was kind enough to make some comments on what I've written on his LibraryLookup bookmarklet in Chapter 1 (which I post here with his permission):

Under "How can it be extended": OCLC xISBN! That service solves a key problem with the bookmarklet version: that an ISBN does not uniquely identify a work. But it creates a new problem: a bookmarklet alone cannot perform client-side remixing (i.e., calling xISBN and then using its output to splice Amazon and the library). I've incorporated xISBN into several solutions:
• http://weblog.infoworld.com/udell/2006/01/30.html

  Being a Greasemonkey hack, this has limited reach. I've been meaning to try to produce a universal version that'd work with IE, probably using Turnabout (http://www.reifysoft.com/turnabout.php), and you've reminded me to prioritize that.

• http://weblog.infoworld.com/udell/2006/01/26.html

  This is actually a different kind of mashup, involving Amazon wishlists. It's very cool. But again, it has limited reach in the sense that RSS notification is geeky.

• http://elmcity.info/services

  This version eliminates RSS in favor of email, the idea being to appeal more broadly. Except it hasn't, because the conceptual barrier -- multipurpose your Amazon wishlist in order to receive notifications about availability in your local library -- is formidable.

  All three of these solutions could, and perhaps should, be generalized for multiple OPACs and multiple libraries, in the way that the bookmarklet generator has generalized the bookmark hack.

  That's it! Hopefully somebody will read this and take on one or more of these challenges, in case I don't get to them.