Aren't CD cases slightly heavier on one side? There's a pivot mechanism on one side and not the other; the CD isn't placed at the exact center of the case; and the paper insert (as well as any staples it contains) can also affect the balance. So you might be able to extend the tower a few millimeters more than what mathematical algorithms allow, by aligning the heavier side toward the desk.

Sure, but this is physics, so we can stick with our spherical cows and other first order approximations without losing too much sleep... :-)