I have had a number of instances where I am trying to restart my G5 (10.3.6) and the Finder tells me Shut Down timed out because the Mirror Agent would not quit. I tried to Force Quit and nothing by that name was listed. I use the Process Viewer (Activity Monitor, whatever its called now) but I couldn't find anything called Mirror Agent there as well. I am guessing that it is a service related to iDisk syncing (the name makes since, and I recently created a local copy of my iDisk and sync is automatically).