http://www.networkworld.com/news/2011/041111-amazon-cloud-supercomputer.html

Without much fanfare, Amazon officials last year built a supercomputer on the EC2 cloud service that placed 231st on the most recent Top 500 list of the world's fastest supercomputers. The 7,000-core cluster, de-provisioned soon after running the Linpack test, used Linux, Intel Xeon X5570 processors and a 10 Gigabit Ethernet interconnect. Amazon's James Hamilton said the Top 500 run proves that a cloud service can be used to build "One of the fastest supercomputers in the world for $1.60/node hour."