As outlined over at Digital Inspiration, you can tap a free (for now) Syncplicity account to designate a local folder as shared: Your Google Docs files will get downloaded to that folder (thus giving you an offline backup), where you can edit them using Word or your word processor of choice. Meanwhile, any newly created documents stored in that folder get synced to your Google Docs account (thus giving you an online backup). All this happens automatically and transparently. Not too shabby, though for now you're limited to text documents -- spreadsheets and presentations aren't supported.
Frankly, I can't understand why Google doesn't build this kind of functionality into Docs. Google Gears hasn't seen a significant update in quite some time, so for now you're stuck using a third-party service like Syncplicity. Free accounts net you 2GB of storage, but it sounds like that's a temporary offering.