This problem goes for #9618 and the #9572 where I've tested this behavior. I've got a large flex app and when I open some of my mxml files I see the memory usage shoot up to my allowed maximum. Upping IntelliJ's mx value to 500M only delays this problem. I look at my CPU usage (quad-core Xeon) and observe what appears to be a single thread that is hogging whatever core it's on. It jumps cores now & then. IntelliJ is basically unusable at this point. The colored square at the top-right of the editor is unfilled and never becomes filled (green/yellow/red).
FWIW I sent a performance report and it's named perf_9618_dsmiley_20090105-105455
I'm experimenting with using JDK 1.6 but that hasn't helped.
~ David Smiley