So, I have been using the current build of Defraggler (v1.02.078 RC2) on XP and Vista, both physical and virtual machines, and all has been "issue-free" for me so far.
This morning, I turn one of my Vista machines, and "Problem Reports and Solutions" notifies me that Defraggler has a "Program Compatability" issue. Perhaps this is something that can or already has been looked at by Piriform developers.
Please know that I completely understand that Defraggler is in beta, so I am not expecting it to work to perfection. I also understand that this happened on the Vista platform (LOL). All I am interested in is sharing a "Defraggler on Vista" experience. After all, isn't that one of the purposes of being a beta user?