I have created this simple capx to test the retina display on my iPhone4. I made it so it can fade-in and fade-out a sprite when touching/releasing it.
There is a problem when using the touch object. You have to touch right and down the sprite to trigger the touch. I would think it this related to the retina display (640 x 960) vs the physical resolution (320 x 480)
Here is my capx: iPhone 4 Test