I'm surprised it hasn't been mentioned yet, but there's a large collection of lovingly formatted files in the ebooks uploads section. If you want HG Wells' "The Time Machine" you can try the copy here on
mobileread!
All the books in the ebooks uploads section are public domain or author submitted and since the formatting is done by volunteers, the work is better than most publishers. While it doesn't answer your question about Google Books (Never used it myself), its a fantastic source of PD books.
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Crafty Dan <><