I use Duolingo ever day. Their app/website is heavily gamified to the point where I think it's part of their tagline. But, at least for me, language learning is fun. When it's not fun it's at least engaging and/or challenging. I don't know if gamification can be painted over fundamentally miserable modus operandi.
Agreed, gamification might be a bad idea in a work context (where it's imposed on people who are competing with each other), but I think it's still a really useful tool for individuals who need a little extra motivation. I usually classify myself as a person who hates exercise, especially cardio, but I'm playing Zombies Run right now and it's great. I find myself doing more than the workouts require to get the extra bonuses/achievements. Meanwhile my free weights (the only exercise I've voluntarily done, previous to this) are still gathering dust in my closet. (Anyone know a good weight training game? :))
