Was the long awaited release of Apple's new and improved OSX, Leopard, a bit pre-mature? Mediocre reviews seem to back up my answer with facts quite nicely.

From Tom's Guide:

"In Leopard, when Finder moves a file from one drive to another, it deletes the file from the originating hard drive, without first checking to see if the file arrived safely on the destination hard drive. If anything goes wrong during the file transfer, such as a momentary power glitch on the destination hard drive, the file would then be destroyed on both hard drives."