I'm throwing this story out there in case anybody is thinking about any of these issues. I installed the latest version of smcFanControl on my mac pro. I had been using temperature monitoring software to keep track of the temp of the processors and 4 internal harddrives (two set up in a RAID). The harddrives had been running between 45 and 50 Celsius, even at idle, and this seemed a little high to me based on what information I could find on the topic of harddrive heat and lifespan. So, I installed the fan control software. Instead of the normal fan speed of 500 RPM i've got it running at 1000 RPM (as a minimum), which is just a little louder, but does amazing things to the temps. If i'm pushing the system at all, such as watching HD movies off the RAID (while de-interlacing the video), I'll push up the fan speed to 1500, which is still quiet enough not to be a bother. The drives are now running around 30C even at a good load. Not good with the Ferenheit Celsius conversion off the top of my head, but I think that is pretty much ambient room temperature. I was less worried under about the CPUs, but even under full load for all 4 cores (running Rosetta@home) they are running about 10-15 degrees Celsius cooler. With the software, you can set the minimum fan speed up to 3000 RPM, which doesn't seem to get much more of a cooling gain, and sounds like a jet engine, so I don't really use that setting.