hmm .. Never knew the Windows Defrag was good..
Honestly, I believe only ppl who do not know that there are 3rd party apps for defragmenting HDDs / ppl who do not have internet access use the inbuilt defragmenter....
Or people who get sick of crappy online and crappy third party ones crashing who keep their drives extreemly anally organized use something that came free and does a decent job at it.
Back in older versions of windows I used third party ones but XP's does a decent enough job of it that I dont feel the need to rush out and buy a utility just for defragging.