David Martin at Cult of Mac:
Exchanges are a bad idea right now. I recommend that you wait. If you have an iPad 2 that is usable, donâ€™t rush to replace it. Youâ€™ll be wasting your time. I donâ€™t think Apple can deliver an iPad 2 with a good display right now.
It seems there is a backlight problem in more than a few iPad 2s.