I've been having freezes of my machine quite regularly, when Java goes nuts and eats all the CPU and memory, so I finally decided to do a dist-upgrade to see if that would fix it. Everything went smoothly, but it didn't actually solve the problem. In the end, I upgraded my Tomcat from 6.0.20.0 to 6.0.26.0, and that seems to have solved it. Must have been some kind of memory leak in Tomcat. But I've also moved the projects I'm not actively working on out of the webapps folder, to reduce the load.