my 24" cinema display from 2010 developed dust/ stains in the lower left corner of the display after about 1,5 years in use. see the attached picture. the problem is mostly seen in imacs. there is a long thread in the macroumors forum describing this problem and showing a not easy solution.http://forums.macrumors.com/showthread.php?t=1101370. i'm convinced that there is the same problem with some of the ACD like mine. probably the cause oft his problem is the sealing between display and backlight (see the description by oggy in the above linked thread) which allows that circulating air can bring dust between the two panels. it looks really like a design flaw. if you are in guaranty apple will change the panel. without guaranty no chance of help. but even the panel is changed the problem can occur again. but there are some hints that apple is investigating this problem. please post your experiences how apple is handling your case if you have the this problem.