Sez LibraryJournal.com:

Google Book Search has just unveiled two innovations: one provides links to Worldcat.org and international library catalogs, while the other allows users to download out-of-copyright books. So far reviews from librarians have been mixed. Downloadable access seems to be hit or miss, with no real pattern for finding which books are available.

This was news on the Google Book Search blog right at the end of August – here’s a quote if you missed it (of if you didn’t know they HAD a blog):

You’ll find everything from classic novels to ancient philosophical texts, to any number of practical or creative works that have entered the public domain since the earliest days of the printed word.

To easily locate public domain titles you can download in full, simply select the “Full view” radio button on Google Book Search, then click the new “Download” button that now appears on out-of-copyright titles.