Over the past two weeks I've spent some time with friends who are investigating Amazon's EC2 service. I must say that I'm very impressed. Essentially the service allows you to run a virtual computer. You can then add and remove hosepower via web service calls, and all you pay for is the uptime per hour, and bandwidth.
I believe the service is either running Xen, or is based off of it. Either way, what they have done with it is truely amayzing.None