We have pretty fast dual CPU machines at work, but I've found the latest few builds of IDEA to be very slow, especially when swapping from one file to the next. IDEA regurarly pauses for a few seconds.
However, I have found the same builds run at an acceptable speed on my personal two year old, single CPU notebook.
This morning I downloaded build 3429 and noticed a slow down after just a few minutes work. I then, using the Task Manager, set the CPU affinity for idea.exe, restricting IDEA to a single CPU. Since then IDEA has performed without any of the slow downs I noticed in recent builds.