Note: This review addresses v4.09 beta.
Once a Mac-only open source application, the v4 release of Cyberduck is now available for Windows too. The application started out as a simple File Transfer Protocol (FTP) program, which most people use to upload files to Websites, but has since grown to be a general-purpose upload and download tool that can connect to a variety of services--including Google Docs' file storage area.
Download the public beta of version 4 and install. To set it up for Google Docs, you'll need to create a bookmark. Click the Bookmark menu, then New Bookmark and, in the dialog box that appears, select Google Docs from the dropdown list headed FTP (File Transfer Protocol).
Then, in the Google Account Email field, type your Gmail address. If you use a Google Apps for Business account, enter your domain email address instead (i.e., email@example.com). Don't change the contents of the Server field! Finally, close the dialog box by clicking the "X" at the top right corner--there's no need to save the data because this is done automatically.
Then click your new entry in the Bookmarks menu. A login box will prompt you for your password, and ensuring the Save Password box is checked will mean you won't get prompted in future.
You should then see a list of your Google Docs files, the same as usually appears in the Google Docs organizer. To download any files, just select them in the interface and click and drag them to the desktop. You can drag and drop multiple files in the usual way using Ctrl and Shift to select files. (Note: An my system I didn't see an outline of the file icons as I dragged them to the desktop, but releasing the button started the download. I presume this is a bug that will be fixed soon.)
To upload files, click the Upload button on the toolbar and select them in the dialog box that appears. Again, you can use Ctrl and Shift to select multiple files. Note that, unless you have a Google Apps for Business Premier account, you'll only be able to upload office documents. The type of files you can upload are listed here. Attempting to upload any other kind of file will show an error message when the upload commences.
Note: This program is donationware. It is free to try, but the author accepts and encourages donations towards further development.