It works, but as with all things technology based, it has its quirks and is only really useful in light traffic (otherwise, if someone pulls in the lane between you and the car you are "following" you will slow down rather quickly. Likewise, if the car you are following moves out of your lane the engine will rev and you will jump ahead to your normally set speed (if you were going slower than that because of the car you were following).
It is best for long stretches of highway without much congestion.