iDefrag is a special program for defragmenting the hard drive on a Mac. It analyzes the hard drive first and then proceeds to the defragmentation. It includes user and system files to speed access to them. You can continue working during the de-fragmentation as the program make a minimal use of your system resources. It has a temperature controller that stops defragmenting when the temperature is too high. The demo version is downloadable if you would like to find out more about the program.
iDefrag Demo-2.0.zip, iDefrag Demo.zip