The reason for the default setting of the jbossweb-tomcat55.sar/META-INF/jboss-service.xml UseJBossWebLoader attribute to true was to allow the use of aop in web envrionments. This is not a prevelent usecase, and with jdk5 instrumentation does not require a jboss specific class loader. Combine this with the fact that users tend to treat wars as dumping grounds for jar files regardless if they are needed and two common problems show up:
1. There are classes that cannot be overriden from a scoped war and so the war class loader needs to be able to ignore attempts to override classes like commons logging. This is most easily done with a custom tomcat class loader.
2. jsp page class names are not sufficiently unique to allow for multiple wars with the same jsp file names to coexist in a flat class loading space. You'll see random errors like one index.jsp servlet class from another war being used with the result being anything from the wrong content to exceptions due to the wrong execution context.