I own two imacs, one 20" and a 24" (both white models, late 2006, early 2007). First I had apple assistance to replace three times (3!!!) the display on the 20 incher, because of stains appearing in the left corners of the screen, now it's the turn of the 24", which displays stains in the upper central part of the screen. I don't know if it's only bad luck but I'm quite convinced that it has to do with the quality of the sealing in the iMac displays (it's dirt sneaking inside the display, I guess). Fortunately I have apple care, so there will be no extra costs. But, it's incredible how this can happen so often. They should do something to enhance their quality control.