Something I just noticed: My MBA was screen saving with the Arabesque screen saver, and I could hear the fan going like a bat out of hell. So I moved the trackpad and the screen saver went away. I immediately pulled up iStat Pro, and the fans were pegged at 6200 RPM and the CPU temp was around 150 degrees. Within just a few seconds of doing this, the CPU temp dropped a full 15 degrees and the fans began to slow down. After just a few minutes, the CPU temp was down to 122 degrees and the fans were back down to the usual 2500 or so RPM. So, hypothesis: Anything that performs intensive screen processing, like a complicated screen saver, will cause the CPU to heat up. This in turn will cause the fans to speed up. One test would be to not use a screen saver at all, but just let the screen go black. If the CPU doesn't have to push a ton of pixels around the screen, it shouldn't get hot, and the fans shouldn't come on.