No backup strategy - it's been working so well for me for over a year now, that if I wasn't posting in this thread, I would honestly have forgotten all about it and wouldn't even remember how I set it up!
One thing that I considered with one person was to backup our tdrives with each other, so as long as we both didn't get booted at the same time, we'd have access to our content - we might get around to sorting this one day.
I guess I'm assuming that if Google ever pulled the plug I'd have a few days to download what I want and to decide if I want to build a new server with 350TB+ of storage to hold everything....