If you are an application developer I would reccomend a standard book on J2EE. If your application is a J2EE application you should be able to design and implement the majority of it without needing to look at application server specifics.
The reason that people write bad reviews for the JBoss documentation is because they were expecting a book that teaches them J2EE from the beginning.
How to write J2EE components has been covered loads of times already, the JBoss documentation just looks at how to take advantage of JBoss specific featureds.
I figured out how some things work by using the openbook Mastering EJB 2.0 from TSS.com and the workbook examples of Enterprise JavaBeans(O'Reilly) by having a look at the JBoss source-examples.
Having a look at the various JBoss books reveals that parts of the Administrators & Developpers guide have been copy'n pasted to almost all other books offered (Quickstart Guide, ....).
Using JBoss is somehow a try and error game.