Layback Bear is correct in observing that Windows 7 already has a capable defragmenter.
Also remember that drive optimization with NTFS is more sophisticated than many years ago with the FAT file system. Compaction was important with FAT, as the allocation table is at the start of the drive and has a fixed location and size. Crowding all the files as close as possible to the start and leaving the rest of the drive completely empty was the best way to secure performance.
NTFS locates the MFT (Master File Table) part-way into the drive to enhance performance, and its size is dynamic. There is an area ahead of it that files will not move into (to allow the MFT to expand), so this will often appear to be non-contiguous free space. Also, as the drive fills, the MFT may be expanded into more than one piece (a fragmented MFT). If this happens, the defragmenter will place the files closest to the fragment of the MFT they reference, so head movements will be smaller in accessing those files. This can actually improve performance compared with if those file locations were recorded in the original more remote MFT location, but the drive will look as though it needs defragmenting.
Edited by Platypus, 28 March 2010 - 09:16 AM.