From Download Squad:

Google Book Downloader is a free utility that lets you download any book that's available in "full view" from Google Books. Of course, most of these books also feature download links right on the web page, but Google Books Downloader lets you queue up multiple jobs and convert all of the downloaded books to PDF files.

The application is available for Windows and requires Microsoft .NET Framework 3.5 SP1. You can either install Google Book Downloader or download a portable version which you can simply unzip and run from your hard drive or a removable disk.

In order to queue up a book for download, just open the "add book" dialog in the file menu and copy an paste the book code, link, or ISBN number, click search, and then select the book that shows up. To begin downloading, right click a title and hit "start." and to export a file as a PDF, right-click and hit "export."

You can find more instructions in the tutorial.