Going to quote Ev again today, with his comment:
Balance controls on stereos, car radios, walkmans, mp3 players, etc. usually have far more prevalence than they deserve. They often compete with the volume control for attention. But how often do you really want to adjust your balance?
I just can't say how much I agree with this statement. All week, I've been learning all the details of skinning Windows Media Player 7 (don't ask...) and I've had to explain why the balance control should pretty much be omitted.