AWS launched a new service called Amazon Elastic MapReduce which provides cost-effective ways to run vast amounts of process. It uses the same kind of developer friendly API designed for Amazon EC2 or S3 for running . You submit a job request along with number of instances to the API, then the status is reported back through the API. You can cancel or modify jobs using the API, and can even add additional steps to a running job.
It looks like Amazon Elastic MapReduce will evolve into a powerfull tool. You can easily offload backgrond processsing of apps to Amazon Elastic MapReduce.