I have seen several discussions regarding performance and none of them really seem to address the issue. I work on a pretty fast workstation (HP Compaq Elite 8000, quad 3GHz, 4GB) and I have seen the performance drop significantly as we have moved up through the versions, especially from 9 to 10.5.1.
It's difficult to put a test case together as the code we work on is protected but it is pretty much only JDK 1.6 SE with I would imagine to be average if not small sized projects (class files < 1000 lines, about 100-200 classes in source, 30-40MB worth of dependencies). I'm not using any frameworks and it is pure java source files.
Class completion popups are unusable, code inspection lags by 5-10 secs and goto class/file actions also lag by 5-10 secs. I find that I am restarting IntelliJ several times a day to try and squeeze any performance and have only started opening one project at a time now.
My colleagues (+-30 accross different teams) share the same experience where everyone agrees that it seems to have gotten worse with every release.
Happy to try any suggestions.