Google Books and Google Maps

It is interesting to think of the things you can do if instead of a bibliographic record containing metadata about an information resource, it actually contains all the contents of the information resource.

One thing Google is now doing with its expanding collection of scanned books is creating maps on the search result page that highlight all the locations mentioned in the book. See the bottom of this page for an example. As Lorcan Dempsey points out this system is far from infallible (for example giving a map of St. Augustine, Florida when the book references the Bishop of Hippo not the city named after him). However, when it works it could be a very helpful way to evaluate the book.

Notice each marker on the New York map in the linked example contains the context from the book where the location was mentioned. I'm guessing this is only the beginning of creative uses of the scanned data. Has anyone actually found features like this in Google books or similar collections helpful?