Though we never deployed directly to Amazon EC2, we have deployed 0.9.6 and early releases of MODx Revolution to EC2 via
RightScale, and though it takes a little more organization and planning, it’s basically no different than deploying on a traditional server instance. You’ll probably want to use EBS for persistent storage requirements, like PHP session data and your web assets, but in general, it’s no more difficult than deploying in a load balanced situation.
Unfortunately, since I haven’t used Amazon’s EC2 management services directly, I can’t really offer details of how to do the deployment.