How does runtime performance compare between JDK1.1 and JDK1.2 on Linux?
(As an experiment, I once wrote a simple non-graphical "Hello World" program and a trivial AWT application, then ran them and watched class-loading activity. They loaded, respectively, 44 classes and 140 classes when run under JDK1.1. The same applications under JDK1.2 loaded, respectively, 180 and 450 classes. These differences map to significant differences in startup time and memory costs.)
The good news is that a lot of work is going into the JIT technology at IBM and Sun, and the current JDK1.3 releases from those vendors are showing improvement. But you still need a lot of memory.