Google Book Search is a good way to find books and then buy them or borrow them from a library. Now the site includes the option to search library catalogs: you can either use the advanced search or look at the bottom of the search results. Google says there is a pretty good chance that libraries are close to you, but that doesn't happen all the time, as Google has information only about libraries from 30 countries.I think it would've been much better to show the libraries where a book is available on the book page, right next to the bookstores where you can buy it.
Related:
Google's Digital Library of Alexandria
How to use Google and become a better student
