Hello, i am working with those two commercial defraggers for some time already, and recently my preference was always towards DK11. (Btw. i have the latest versions/updates of any of those defragmentation programs). I have reason to believe that the latest DK (.781) messes up my MFT or does something else weird to my filesystem under Vista SP1. I got a new HD which i tested out ok, so it doesnt have bad sectors or anything. Running Diskeeper it already happened twice in a week that my MFT was corrupted and i got various messages in event viewer in regards to filesystem corruption. I had to play back 300GB backups two times already. I have reason to believe it MIGHT have to do with the MFT frag-shield of diskeeper. I deinstalled it now since in the latest version .781 ifaast was at "pending" for days already....and boottime defrag was disabled anyway "due to incompatibility with SP1"...so it was kind of pointless. So...right now my filesystem is ok and ever since i deinstalled DK i didnt have any corruption anymore - so i strongly tend towards PerfectDisk at the moment until DK fixes whatever is going on there. I really like(d) the fact how diskeeper made an intelligent free-speace consolidation using i-faast and was placing seldom used files at the end of the HD. This resulted in the nice benefit that free space was always in the middle/beginning of the HD...therefore no "degradation" of the HD over time. PD i like very much since it does a better job in off-line and metadata defragmentation....but even with the latest PerfectDisk i dont like the fact that PD always uses "old-style" consolidation and consolidates/defrags all files in ONE block at the beginning of the HD - with the free space at the end. This is especially noticeable if you have eg. a 500GB where there is only, say, 20% free. So..the end of the HD is approx 50% slower in terms of transfer rate....and PD would leave the remaining free space always at the end, thus making new writes to the HD slow. Right now i deinstalled DK, i use/activate PD only if i think i need to defrag my meta-data..and i will observe how my filesystem is doing right now without Diskeeper which otherwise i liked very much. G.