This seems more like a DailyWTF than a sweet optimization to be reminiscing about. I'd love to hear more details about this. I mean a single video is about the equivalent of tens of thousands of 404 pages.
I'm not sure which is more mindboggling... Spending 66% of their bandwidth and 50% of their CPU on serving these trivially cacheable pages or the fact that they didn't correct the problem when they were serving more than 5%.