Google’s reliability is amazing. Their servers rarely go down, and I would go so far to say that their archiving and storage capabilities are nearly flawless. But despite Google’s dependability, they aren’t infallible – Google Apps users are still losing important info every day.
Now, we don’t really think that your users are foolish, because anyone can make an honest (but irreversible) mistake. We simply know that you will face situations where Google can’t save the day.