There was a time a few years ago when I was absolutely certain that the world was going to return to sustenance level living really soon ( http://en.wikipedia.org/wiki/Malthusian_catastrophe ). And then I read The Road and got extremely depressed. So I've thought about this a lot, and even asked someone (who you may have heard of) if there was already a system or procedure in place so people could keep in contact aft…
Someone else had it right too, if there were a large enough catastrophe to knock out the infrastructure supporting the internet entirely - you would be concerned with many other things.