Surprised Tumblr didn't make this list after the incident in early December where they had more than 12 hours of downtime.
Ahh great call totally forgot about the DDoS attacks those 4-channers put on tumblr.
I guess the lesson learned from the tumblr downtime is don't piss off 4Chan
in this article, I cover briefly why these big sites had downtime in 2010. I offer simple advice to a non-technical crowd on how to avoid certain mistakes. Obviously, the situations at all of these sites were pretty complex