Cool new Amazon feature: Amazon.com Citations.

Amazon scans every book in the Search Inside the Book program looking for phrases that match the names of books in our catalog. We make a note of these "citations" and display them to you...

For example, a book I'm currently reading—Moral Animal—contains references to 96 other books. This feature can help situate books within a larger context than the Customers who bought this item also bought-list can. I hope they make this data available through the API so we can see some Touchgraph maps of book-citation connections.

And they should start scraping the URLs mentioned within books too. And while I'm wishing, how about citing weblogs that cite books? ;)