One of the great things about compute clouds such as Amazon EC2 is their elasticity - you can quickly and easily launch as many servers as you need. And, with Cloud Tools, you can easily deploy and manage your Java/Grails applications on Amazon EC2. A recent blog post by Dustin Whitney describes the benefits of using Amazon EC2 and Cloud Tools. His Grails application, which was running on single instance, was overloaded by a sudden increase in traffic. Fortunately, he was able to use Cloud Tools to quickly redeploy his application on multiple instances that could handle the load. Another success catastrophe was avoided!
Also, as Dustin mentioned in his blog, he recently added a lot of new features to the Cloud Tools Grails plugin. It now has the same extensive set of features as the Cloud Tools Maven plugin. New version of both plugins have recently been released. New features including support for using Elastic Block Store as the database and deploying static content on Apache.
I hope that you will try Cloud Tools. Or, if you are looking for even more ease of use including the ability to deploy your applications with a few mouse clicks and features such as monitoring then check out Cloud Foundry.