On the positive side, I do not double-book ressies and if we know that we are not going to be in the park that day then I will cancel the night before or that morning on the bus ride.
With that being said, I will be the first to admit that I have no intention whatsoever to pull out my cell phone and cancel if we spontaneously decide to deviate from the schedule. I know we're only talking about one or two minutes, but I am not going to press "1" if I have been to WDW before, then press "2" if I haven't been since 1994, then press..... while strolling with the family in the Magic Kingdom.
Let the flames begin.