When your site is down what do people see? If overloaded to you respond well or not?
For much larger organizations with the infrastructure and DNS management this should be part of your DR strategy. Yesterday was FireFox Download Day. Mozilla I don’t think coped as well as they could have and were not prepared. Looking at the two screens below you can see examples of error pages I got.
In this case it was a planned event, the increase in traffic was predicable ahead of time. Surely they could have had a static pages with something about the event, the high load and even then a static page of links if your goal was to download FireFox 3.
My site certainly doesn’t support the automated failover, I have to make a DNS change at my domain register Go Daddy to a different host that is already ready and wait for delegation, but I’m prepared for a significant outage like previously.