Why there's a white shadow on top of the black one? Doesn't look natural.
I wrote a blog entry a few months ago on how to achieve realism with respect to digital light sources, maybe it'll help someone out: http://flyosity.com/tutorial/crafting-subtle-realistic-user-...
The author's idea of realistic lighting effects indeed doesn't take into account the perspective of the curl on the note, and therefore looks a bit unnatural.
P.s.: Great post.
I agree that it doesn't look quite right, though.