Hi,
I just wanted to share my experience with Defraggler.
After running defraggler 1.10.143 I restarted my computer (Windows XP SP3) and I got a blue screen of death with error message STOP 0x00000050.
Based on my knowledge I suspected a corrupted driver file issue and started by uninstalling the video driver (in my case ATI Catalyst) in safe mode. After rebooting with "last known good configuration", Windows told me it has recovered from a fatal error. I then restarted computer in normal mode and reinstalled my ATI video driver. Everything was then back to normal.
I hope this helps.
Bidonet