Good news. Google has finally released an API (?) for Google Book Search:

Web developers can use the Books Viewability API to quickly find out a book’s viewability on Google Book Search and, in an automated fashion, embed a link to that book in Google Book Search on their own sites.
As an example of the API in use, check out the Deschutes Public Library in Oregon, which has added a link to “Preview this book at Google” next to the listings in their library catalog. This enables Deschutes readers to preview a book immediately via Google Book Search so that they can then make a better decision about whether they’d like to buy the book, borrow it from a library or whether this book wasn’t really the book they were looking for.

Tim Spalding of Library Thing has some initial comments on limitations:

The GBS API is a big step forward, but there are some technical limitations. Google data loads after the rest of the page, and may not be instant. Because the data loads in your web browser, with no data “passing through” LibraryThing servers, we can’t sort or search by it, and all-library searching is impossible. You can get something like this if you create a Google Books account, which is, of course, the whole point.

(via Peter Brantley)