"Gamification" is a new thing in productivity circles - I believe it comes from video game designer and philosopher Jane McGonigal. McGonigal has dedicated her life to analyzing why we love video games so much, and why they are better than real life.
One thing games have over real life is a reliable - yet variable - rewards system. Every time you harvest a crop in Farmville, kill a monster in World of Warcraft, or shoot an alien invader in Halo 2, you get points. As points accrue, you level up and get rewards. Leveling up usually means getting some visual symbol to show how far you have come, and rewards can be anything from better fertilizer for your crops to a more effective weapon.