To clarify - the hard part is not the destruction of data you know about, it's the identification of data on devices you don't know about, or forget.

Computers with hard disks are obvious, but also consider mobile phones, tablets, games devices (that increasingly ask for sensitive information), PVRs, and so on.

There may be a point, if we haven't already reached it, where I can't dispose of a toaster without worrying about how to wipe its memory.