[justizin]

At Rackspace - some time ago, I can't speak for now - the most common phone call we received was:

  "My site's down!"

Ninety-some percent of the time, the customer's internet was down, or the internet in their country was down, or they were in Europe and the Sprint link across the Atlantic was down, or there was a problem with DNS.

There's a notorious video of one of the founders, barefoot, teaching a class about DNS for the relatively non-technical folks we hired for first-level support triage.

This would be a great supplement, the moral of the story being, these days, if you support any service on the internet, you support every internet service provider that exists. ;)