I've been feeling good lately about drinking diet soft drinks. Then I read this in The New Sugar Busters:
[P]hosphoric acid, which is present in most soft drinks, can interfere with the efficient absorption of calcium. It is easy to see why our children are not developing the proper bone density early in life and so will be much more likely to have osteoporotic problems, including bone fractures, later on. The fact that the sodas are replacing the consumption of calcium-rich milk or fruit juices amplifies the problem.
I looked at the label on a can of no-caff, diet Coke. Sure enough, phosphoric acid. I drank a glass of water instead.