Google Drive (nee Docs) will automatically backup designated folders now. There's a client to download that will take care of it for you.
While you're at it, the Google Cloud Connect plug-in allows you to save, modify, sync, and share Microsoft Office files in native format. If you're working offline, you can sync your changes to Google when you're back online; and if others alter a file, you can control whether yours should supersede others' changes.
