For the past few releases, Canonical has put quite a bit of energy into making Ubuntu a first-class OS for use in the cloud. Ubuntu now has cloud support for Amazon’s EC2 and Ubuntu Enterprise Cloud (a “private cloud” system based on Eucalyptus). More here

This means that it’s easy to spin up Ubuntu instances on EC2 or to make your own private cloud with Ubuntu … where you can spin up more instances of Ubuntu … there’s a lot of “cloud” going on here!