We only use it on long trips (meaning at least three hours, but not even sometimes for the three-hour trip to my brother's).
I was against it for so long, and we travelled without one on trips to Virginia, Florida and New York.
But now we love it. They still play car games, color, bring GameBoy & Leapster, sing songs, etc. But we work in a movie here and there and it gives us some quiet time.