After updating the listings for electronics, Google Product Search (previously known as Froogle) integrated the data from Google's book search engine. In addition to the list of stores where you can find a certain book, Google shows a summary of the book, the table of contents, references from the web and related books. There's also a link to Google Book Search, where you can preview and search inside the book.
In other book-related news, Panlibus points to Zoomii, a great visualization for Amazon's bookstore where books are placed in virtual shelves. If the products are more tangible, people are more likely to buy them, so Google should show more visual information: images, videos, trend charts, feature comparison etc.