Earlier today, Tyler Hall of Sitening announced that they were releasing a set of open source PHP interface classes for Amazon S3, Amazon EC2, Amazon SQS, and the Amazon Mechanical Turk. The classes are hosted in Google Code, and can be downloaded here.
Tyler also let me know that these classes were used to build Sitening's Basejumpr application.
They actually spool up EC2 instances on demand in order to do heavy duty batch data processing. As Tyler told me:
We couldn't do it with just one server, and being a small company, we can't afford to lease multiple dedicated servers which might sit idle most of the time. With EC2 we launch and shutdown instances as needed. It's typically an automatic process controlled by our web server. But we've also built a control panel so we can start and stop instances manually.
Once again, it is a great example of Web-Scale Computing in action (I'm sure you are getting tired of hearing me say that).