Currently GAE raises a compilation exception of the Roo generated jspx files in a GAE environment. The problem is the use of jasper-runtime-5.0.28.jar in the current version of GAE alongside geronimo-jsp_2.1_spec-1.0.1.jar. This means that GAE have an API which allows JSP 2.1 and an implementation of Jasper which only supports JSP 2.0. Spring Roo generated MVC apps use a number of JSP 2.1 features (mostly EL related) which are supported by all current Web containers but not GAE. (see http://code.google.com/p/googleappengine/issues/detail?id=1506)
As such GAE deployments are currently not supported by Roo generated Spring MVC applications. However, we are in contact with Google to resolve this issue as soon as possible. As a workaround Roo could ship a custom tag library (potentially with reduced functionality) to support JSP 2.0 EL.
Another issue which needs to be resolved is the full support of the default GAE data store. This will require changes outlined in ROO-611 to fully support references between domain objects.