Since I ended up with both white and black A320s, I've had a chance to play on both, and I've found a slight difference between the D-pads on them:
The black model feels slightly raised and has a slightly stiffer feel, a combination that makes it a little more playable on some games and generally the better feeling of the two for me
Let me be clear that the white model is still entirely playable and I have zero problems with it. I love 'em both.
It could be a coincidence or a difference in production runs, I don't know. I just figured I'd throw it out there.