I just started noticing this problem yesterday. The guy in the original thread noticed it when he was an inpatient in a hospital and I am a doctor and I first noticed this while I was at work yesterday. Interesting the problem isn't apparent under sunlight or regular wattage bulbs, but under fluorescent lights, there's a big oil slick appearing square. This was a problem on the touches as well. Does anyone know the cause of this? It never was clearly answered in the thread below, but the suggestion of a leak in the LCD fluid seems plausible.
http://forum.ppcgeeks.com/showthread.php?t=25981