On Data, Backups, and "Cloud"-based Services

If there is one lesson to be learned from the Sidekick fiasco, it is spelled out perfectly in this Chicago Sun-Times article by Andy Ihnatko:

Lesson Three: "If you don’t own and control a local, physical copy of your digital media, then the existence of that media is merely hypothetical."

I appreciate and heavily use cloud-based services, but I know that they and the data they store could disappear on me at any given moment. For example, although I use GMail with Google Apps, I make sure that I control the domain name, and I use Apple Mail combined with Time Machine to ensure that I have a local backup of that data under my control.