I would like to say that this is a great extension and does exactly what it advertises. Unfortunately, it doesn't work at all. It's not clear if the lack of functionality is due to software bugs or changes in the way Google handles its documents. The developer may or may not know, but s/he appears to have abandoned the project. Just look at the support forums on the deveoper's site, and you'll see dozens of unanswered questions. Don't waste your time. I wish I hadn't.
The extension has been Updated and works!
You can get support at the JoomlaCode project page.