Agreed with the efficient filing system to a certain extent. If you are using the Mac for music or video applications and move data all over the place alot, some form of defrag would be good.
For me, I use the good old copy, erase method. I have had bad things happening to my drives with defragmentation software. Nothing beats cleaning up the platters the good old formatting way. This is why I love Mac. Tell a PC dude to got format his hard disk and most likely he will give you the finger.
