Defragmentation can free up space, and speed up the computer, but as mentioned, its not effective really by itself, or in a properly maintained system. however, i work in this field as a tech and see computers that are not maintained by their owners at all and are DOG slow. I use a relatively easy system to speed them up significantly, VERY noticeable speed increase, but its usually on systems that have been used for over a year with no deletion of files, no defrag done, and heavy use. The first thing i do is run norton system works, win doctor, this usually finds and repairs on average of 300 problems, then run fast and safe, the next is to run some sort of spyware program, my program of choice is adaware, only a personal preference. Upon removal of those files and items, and the fixing of the problms, i run a program called VoptXP, its an efficient, and very fast disk defragmenter. After all these things are done the computer was running like a champ, and the customer NOTICED it VERY much. But it has to be a pretty far gone computer in order to actually GET a performance boost, and even then its not a performance boost, its just regaining LOST performance. Hope this helps