Macintouch is reporting (as an entry in their continuing OS X Special Report) that, in certain situations, using the command key shortcut to move data from one drive to another can result in data loss. The Macintouch report has all the details, but the situation seems to arise when the destination volume has difficulty accepting the moved files, due either to space or naming limitations.
So for now, if you've been using this shortcut, you may wish to revert to the older copy to destination-erase original methodology. Personally, this is the way that I've always preferred to move files about; even on my Windows box at the office I stay away from the "move" option. I like the security of seeing the files in two places at once prior to erasing the originals!
Apple is aware of the issue, at least according to the post on Macintouch.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020329120845118