"Gamified" e-learning - what examples have you seen or built?

I recently read Karl Kapp's new book on Gamification... it was an interesting read, and kind of cool to think about the possibilities of how gamifying content can make a course more engaging and effective.

Curious to know what your take is on gamifying e-learning ... what examples have you seen? What made them effective (or not)?

Have you built any gamified content in your own courses? Got anything you can share?