And what about when a notebook is encrypted?

Quite. I'm still wondering about ways to make my encrypted backup drives invulnerable to an untargetted attacker who just decides to blat zeroes over every accessible block device. Is there some way to turn the USB port off, then on again? (It's connected to a hub, and I don't want to turn off the whole hub, so this gets a bit trickier... some way to make the blockdev vanish. I guess a simple rm or mv-out-of-sight-to-somewhere-not-in-/dev and then mknod or mv-back later on would do it, but that feels really disgusting.)