I completely agree with all.  I had a sticker system back in elementary and once you received so many stickers, you could pick something from the treasure chest.  My own children earned Pizza Hut pizzas when they read enough books.  The digital component has made it more visible in my opinion.  But, like it has been pointed out, competition doesn't motivate all students and there are aspects of cooperative gaming that could be applied instead of just the competitive aspect.