It's one of those techniques that when it works it works really well. Lately, I've found myself contributing more to Google Maps. Each time you add some info or verify info added by others you get some points. As you earn points you can get to a higher level. Google regularly offers perks to contributors at the highest level, but honestly, that's not been a motivator to me.
Logically I know Google Maps is owned by a huge company and I'm only contributing to their future success. But I've found it so useful in my own life that contributing to it feels less like I'm helping a giant corporation and more like I'm helping someone like me who occasionally relies on maps to get around.
This is the reason I think gamification works so well in Maps. Contributing already gives you an emotional buzz. You feel like you're helping someone. Attaching points and a levelling system that further amplifies those feelings. You want to help others and earn points from doing it. It rewards your initial selflessness by satisfying your own self-interests.
Not every platform has these emotional ties to actions. When many try gamification techniques it feels forced and tacked on. If you can find a natural way to further reward your users for taking actions that already delight them, maybe you can get them hooked the way Google Maps has hooked many.