Peter,
The Java version is 1.6.0.02.
DisableExplicitGC did help with no reported problems from the users. It took about 2 hours for the first full GC and they are now occuring about every 45 minutes. This change alone has resulted in a significant reduction in the number of full collections and time spent in data collection. Based on some of my previous reading, I suspect there may still be room to increase the young generation and further reduce the number of full collections. I'll take a look at the membership requirements for the link you provided and see if the info there can help me out.
Thanks Peter.