The first time I used the offline defrag it aborted (harmless but frustrating) - but I soon found it that this was due to StyleXP. It was tying down some part of the disk that PerfectDisk needed.
So I ditched StyleXP and went for the DIY theme approach, and I haven't had a single problem since.
Admittedly, I only do an offline defrag when PerfectDisk recommends, which isn't very often (maybe once every two months). I have it set to do MFT & paging file etc.
Some points that may be worth noting:
- I'm not using RAID, just separate SATA disks
- The StyleXP thing demonstrated that some software agents (virus and spyware scanners mostly I'd have thought) can mess with boot-time defragmentation. It's probably safer to disable such things prior to the defrag (though I have NOD32 and this does NOT interfere with PerfectDisk at all)