I'll let Alex add some of his own comments here, but we are actively using the CDK now to develop our own components.
The documentation is a bit lacking at the moment, but there are some resources.
Alpha1 Tutorial: http://community.jboss.org/wiki/RichFaces400ALPHA1CDKTutorial
Design wiki page: http://community.jboss.org/wiki/RichFaces40ComponentsDevelopmentKit
We will be focusing more on the CDK docs as we wrap up 4.0 development, but hopefully this is enough to get started. Any feedback, or issues you run into and let us know about would be greatly appreciated :-)
Hello Jay, any updates on resources what can be used to study usage of CDK?
There is nothing really new in this area besides the resources that I stated above.
Dev and Docs teams have been focused on component development and reference. Another good way to understand the cDK is to walk through one of the existing components.
An old thread, but in case anyone comes across it, I'll add that I'm collecting references to the exisitng documentation efforts:
Work on properly documenting use fo the RichFaces 4 CDK is expected to pick up after the 4.1 release.