Switching to Jetty was the best thing we did - Tomcat fell over all the time. Jetty has just stayed up.
I find Tomcat 5 to be infinitely more stable and performant than Tomcat 4, so I can live with that for the moment.
If you ever decide to switch, let me know and I'll send you config samples.
We are in the process of ordering a couple new servers, so we might switch when we install them. But it's more probable that I switch jobs before we switch application servers ;-). Thank you anyway.
Ugo