"Today, December 20th, Ubuntu is running 4,840 instances on EC2, followed by CentOS, with 1,250, Fedora with 313; Oracle with 80; and Red Hat with a mere 73 instances."

Only ~6500 instances up and running on EC2 today? That seems to me to be too low by at least a couple orders of magnitude.

Edit: Their cited source (http://thecloudmarket.com/stats) is a catalog of images, which makes a lot more sense.