If you are using Windows Vista or Windows 7 then such programs are not necessary. The reason being is simple. Vista/Win7 will automatically run Defrag when your fragmentation reaches a certain %. So by running extra software you are in essance causing the system to defrag the drive multiple times causing more wear and tear on the drive. This is especially bad if you use a SSD drive for Windows. You will want to make sure that you check the Defrag settings and have it set to run at either a higher % or turn it off completely cause it will put more wear on the drive and cause it to die quicker.
I have yet to even use defrag since installing Win7. I set it to defrag once my drive reaches 30% and havent checked it since. Cause I know that when my drive reaches that mark, it will auto defrag it for me.