This explains a lot. If my thumbs were 1/3 their present size, moving the blocks around on my iPhone probably would have been a lot easier. I recommend increasing the area you can touch to "grab" a block by at least 50%, and adding some sort of visual indicator of the position and orientation of the block outside the thumb-occlusion. Other than that, it's a great game.
@ghempton, if you're still reading these comments, it's likely you're passing a iOS 4 or 5 message without checking to see if the message is received.
I ran into this recently with a number of simple startup checks, e.g., if the device is a high-res ([UIScreen scale]) or if it's an iPhone vs. iPad ([UIDevice userInterfaceIdiom]).
