I at 60G of just pictures, my 160G backup drive is getting pretty full so I have to exclude a couple things that are not irreplaceable.
But again, the big issue is restoring, you don't know what download speed you may get where you end up, or in my case I know is dial up and 36k max because the phone lines are so long/old/bad you can't even get a 56k connection there so I'd never be able to perform a restore.

If your going to rely on someone else for data backups then why not rely on someone else such as FEMA for food/water, why prepare?