Since using Mac OSX Leopard I observed many applications (muCommander, Transmit, CyberDuck, etc) signaling they finnished some job in a transparent background bubble. I find it a good method of signaling the completition this way since an app with a long taking operation is usually left alone in the background and the operator finds some other task like reading the Camera Bits forums.
,-))
Maybe PM could signal in a similar way it finnished the ingest, FTP upload, renaming, export, convert, save as or the stuff it has done. It would be mostly useful for those operations that lock out the user, disabling to use PM at all.