A few months ago, I wrote of My Cannon SD500 LCD Cracked and my successful self repair for $40.
At the time it seemed that this has happened to many people and to many versions of the Powershot series camera with little explanation other than many suspecting an manufacturing defect.
I recently noticed a possible explanation that would likely explain my breakage (and it wasn't rough handling). The camera comes with a wrist strap which attaches to end of the camera and has a separate sliding plastic piece which allows you to cinch the strap to your wrist (so it won't easily slide off). When I was putting my camera back into it's little case, I noticed that the following could result:
Note that the plastic slider is positioned directly over the LCD screen. In this position it creates a pointed pressure point on the LCD screen and, I fear, any little pressure would cause the LCD screen to crack. This easily explains how my LCD cracked (not that I have any direct proof this happened as I didn't notice the position of the handstrap when I took the camera out of the case).
Moral of the story: Keep the strap on the front side of the camera when you put the camera into a case or don't use the strap.
Let me know if this may have been a part of your problem as well.