I used to frequent a relatively niche forum that I think was built on custom code. I don't know how common this is in the popular forum packages now, but it sta

I used to frequent a relatively niche forum that I think was built on custom code. I don't know how common this is in the popular forum packages now, but it started publishing a list of top posters (by quantity of posts). Gamifying engagement led to a subset of people competing for the top 10 positions and commenting on literally every thread. This was rewarding for a handful of people, but created a worse experience for everyone else. And from the outside, it looked like these people were suffering from serious addiction. I suppose it's a universal truth that a small group can poison a large community when given a poorly (or excellently depending on your view) conceived incentive, but Facebook has shown how well this model scales in the digital world.