Jedit is a great text editor, and I love that it is truly cross-platform. I usually use it on windows and just recently spent a long while working on some stuff on my linux box and noticed a large difference in performance. Switching between buffers, in particular, takes much longer than on windows.
I'm using Ubuntu 8.10 and latest version of Java from Sun, tried using -xms/x from 128M to 2048M and it only seems to impact the time it takes to load the program. I tried upgrading to the lastest jedit in the repos (4.3pre17) but that has not helped either. I disabled all plugins (I use projectview, buffertabs, and a few others) but this did not change anything.
I don't know if this is a jedit-specific problem or a java issue in general; jedit is the only program I run in that way (invoking java on a .jar, etc) Does anyone else run it and could recommend some tweaks to either to improve performance?