my screen has a couple of cracks on the left hand side. I never dropped the macbook or put pressure on it. They just appeared one evening when I was surfing the net. I just use my left thumb to adjust the screen and when I went to the genius bar they told me that that caused the damage on the screen because it is real glass and it is worn. I cant believe that but they would not replace it under warranty. even its just a year old and has 3 years warranty. I’m sure that the screen should be strong enough to cope with adjustments using the thumb on the side. I bet people in the shops always do that. Very disappointed with their decision.