Generic JVM Argument -Xnoclassgc must not be used with the IBM 1.4.2 SDK... EVER

...especially if any classes in your application use serialization or refection.

Does your Java application appear to suffer from memory leaking? If it does, check to see if you have the parameter -Xnoclassgc enabled.
In fact, you should check even if you haven't noticed any memory leaking, and disable it anyway :P

http://www.performancewiki.com/was-tuning.html

http://java.ittoolbox.com/groups/technical-functional/java-l/memory-leak-issue-1458060?cv=expanded#

http://www.flester.com/blog/2008/03/24/javas-xnoclassgc-considered-harmful

and finally, one from the horse's mouth:
http://www-1.ibm.com/support/docview.wss?rs=180&uid=swg1PK63384

It's hard to believe that people bother arguing over this one - it's been common knowledge for over 2 years now.