Diskeeper is still the defrag engine being used by Vista.
Microsoft decided,correctly in my opinion, that defragging was a background operation. It runs on a schedule, or can be used manually, according to how you wish to customise it. After SP1, you also have the option of choosing which partition you want to defrag. The first time it is used, it can take a long time. It is shadow copying whilst it defrags, for you own safety. After that, it runs on you chosen schedule unobtrusively. I have no wishh to see those little squares jumping around, it does nothing for me. The new policy is, I feel, well chosen.
If you want to read up on Crabby's comment, look here:
Features of the Windows Vista hard disk defragmentation utility