I have a quad 2.66Ghz Mac Pro with 4GB (currently 533MB free, 957MB inactive, 664MB/1GB swap) and I have a few apps open (Mail, Safari, iTunes, Adium, Azureus, Speed Download) but none of these are very processor intensive. I also have Folding@Home client running in the background, usually I have about 25% idle processor time (I would have expected less personally) but from time to time this changes to 90%+ for a few seconds at a time for no reason. Usually, if I look at iStat Pro, the idle time stays at ~20-40%, and four Folding@Home cores are doing most of the work, but sometime they'll work hard for a few seconds, then work very slowly and the idle time is ^90% for a few seconds, then back to working hard for a few seconds etc... I thought this might have been a Folding@Home issue, but I tried exporting a video in Quicktime when I noticed this happening, and it happens to Quicktime too (although idle time usually doesn't pass 50%). I know this isn't exactly a terrible problem, but I'm just curious, if it can work steadily sometimes, why with the same apps running does this happen other times? Sorry if I haven't explained this very well, it had to be written in a bit of a hurry.