this idea and think it's awfully cute. I don't know what age is the right age to try this since the older kids might think it's lame, but who knows. Maybe you can put a spin on it that would make it more appealing to the "mature" crowd. If you have a brood of children you could also have a second cube (more authentic to the actual game of craps) and write a name on each side. Whichever name comes up is the spokesperson for the prayer time.
If you aren't Catholic and don't have the selection of written prayers (although I encourage you to check out the "Guardian Angel" prayer and the "Glory Be" especially) you could have on one side, "Pray for a friend" and on another, "What are you thankful for today?". The sky is the limit! And it's a dice game where you'll be a winner every time!