Hey Trevor, I know it's late, but I was just looking at this and wondering what kind of performance enhancement you might get by using elementFromPoint:
http://jsfiddle.net/EuL8t/10/
Where natively supported (not IE pre-9) I would think this could
reduce the number of computations, since you don't care about the
dimensions of anything but the dragged element. Obviously suitability
depends on your game design -- I don't know what it actually looks
like -- but this is a mockup.
-- Sandy
