I noticed today that there is a dust-like shadow in the lower-left corner (see the attached picture). This display was bought in July, 2011. I read many posts about the dust within the display of iMacs and never heard of the dust within an ACD. I called Apple support about this. Unfortunately, they did not register any of my two ACDs under the AppleCare of my Mac Pro (I did send them the serial numbers of the two ACDs together with that of my Mac Pro). I was told that they were going to find out what went wrong with my AppleCare registration.