If you are pushing a Mac Pro, time to fire up Software Update, as Apple has just pushed out the Mac Pro SMC Firmware Update 1.1. What’s it do? Straight from the horse’s mouth:
The SMC Firmware Update adjusts fan behavior in Mac Pro. The updater application will be installed in the /Applications/Utilities folder and will launch automatically. Please follow the instructions in the updater application to complete the process.
So there you have it - fan behavior upgrade. Not too exciting, but still important.