The Deltaset Project is a new generation productivity tool (Apache 2.0 Licensed) for extremely fast implementation of a full blown, java based, web applications. 

It supports Google Application Engine. 

Based on JSF 2.0, using Spring 3.x, Spring Security 3.x,  Deltaset will create for you web ui, RESTful web services (JAX-RS), integration with JAXB, JQuery, JQueryUI. 

The first known project that supports JSF 2.0 with Expression Language 2.2 on Google Application Engine.

www.deltaset.org

Here is the "Quick Start" : http://dmakariev.blogspot.com/2010/08/extreme-productivity-with-jsf-20-and.html

If Deltaset has a version supporting JSF, CDI (including Weld or Seam 3 alpha/beta) then more people will give it a try, I think. Personally, I don't like using JSF and Spring very much. If I go with Spring, I'll choose Spring MVC. By the way, PrimeFaces works on GAE (if you want more JSF components).