Is this the worst possible bug ever in an OS? Possibly not, but at least it's not Windows, for once. In Mac OS X 10.5 (Leopard), if you use Finder to move files (not copy), and for some reason the connection to the drive is lost (let's say you lose your wi-fi connection; somehow knock your USB flash drive out, etc. etc.), the data which was not already copied will be lost. It's as though the OS thought the copy completed successfully and it deletes the source files.