I originally posted the following paragraph to the errata page. I apologize if that was inappropriate.
Regarding your design that uses metadata files for integration with Spotlight and Quick Look, it seems there might be some user confusion regarding these files. Users could easily conclude that these files actually contain all of the data for the recipes. This could lead users to do things like send them to friends as email attachments, delete them, rename them, etc. with various unexpected results and confusion. You might want to mention these potential drawbacks in the book.
It would be great if Apple provided a more direct method to integrate Spotlight and Core Data. Does anyone know if Apple has any plans to do this in Snow Leopard? Spotlight’s file-oriented nature seems to be an inherent problem for database-backed applications.