Basecamp/SignalvsNoise/37signals had an article up on how they used Dyn.coms DNS service to achieve something like this, but I can't seem to find it. They had some nice graphs for when they tested it out.

Edit: My Google skills are poor, but I found it here: https://signalvnoise.com/posts/3857-when-disaster-strikes

Thanks for the -1 on a true statement about my own hosting setup!