Available option in deploy/jbossweb-tomcat.sar/META-INF/jboss-service.xml
This configuration options toggles usage of separate classloaders for web modules. The JBoss unified classloader holds all the classes from multiple web applications in one big classloader and may cause unwanted interference.
Imagine web modules "sales.war" and "stock.war", both containing some version of "utility.jar". In case "sales.war" uses version 1.0 and "stock.war" requires version 2.0, turning off the unified web loader is the safest solution. If you don't, the first loaded library will have priority, and remains in the classloader till the reference count drops to zero.
The disadvantage of using isolated classloaders: either you need to duplicate the same library across multiple web modules, or add it to the classpath of your server instance (default: lib/). The instance libraries are defaults, they can be overridden when the web module contains it's own custom versions.
The configuration file contains a small comment about isolation of JSP files as well, to separate two JSP files with the same name from two different web modules. In JBoss 4.0.5, using non-precompiled JSP pages, this seems to work fine, even with the JBoss unified web loader.