Decided to try and install bootcamp for kicks and ended up not being able to do it because my large Fusion image was fragmented (bootcamp is picky). The solution from Apple was to backup the hard drive, reformat, and restore the backup image. This will result in your entire disk being consolidated with no fragments. i did this and have noticed that my Logos under Fusion runs even faster than before (note that I was pleased with the way it performed before). My overall machine is much snappier but the Windows image absolutely flies with Logos.
Apparently the few utilities out there for Mac OSX don't really do the full job (at least according to Apple) which is why they recommend the full reformat. YMMV.
BTW, Bootcamp is faster still, but not hugely so, to my surprise.