I want to strongly second that. I was digging around the code for weeks now to figure out some of the basics (e.g. how to initialize a JBoss Module, how to create and register a service, how deployment works, etc.) but are still completely lost.
Good documentation from the community was a hallmark of previous JBoss versions but I have a feeling that this is not the case anymore.
All what is needed would be some basic high-level documentaiton from some of the "insider" and we - the community - could pick up the ball from here to add more documentation.
My two cents...