[jyl]

Last two things I can think of - if you are using Time Machine or .Mac sync (MobileMe now), and have an older/slower machine, it can slow down when those tasks are running. I have a G5 iMac and the performance hit is apparent at those times. Though, it is a "slowing down", not an "acting weird" issue. Finally, if you have a family of dust bunnies in the computer, blow them out - don't want to interfere w/ cooling. These are probably not the cause but can't hurt to mention.