I noticed a lot of performance improvements when I upgraded JDK from 1.4 to 1.5 and JBoss from 3.2.1 to 4.0.2. With the old setting JBoss memory usage used to reach 1.5 Gig about two weeks after deployment so I had to restart the server everytime it ran out of memory. But after the upgrade, I have not seen any memory problem. Garbage collection improved a lot. Not sure if it is JDK or JBoss.