In my first, the markup was littered with urls looking like
http://www.domain.com/path/to/stylesheet.css?v=20
After a couple of projects I noticed that the number was decreasing. As I was learning to work with their fucked-up FBML/FBJS/weird-corner-cases my code went through less and less iterations and the final numbers were lower and lower.And I was a little happier inside.
That's gamification, but unintended.
Making it part of the product? I'm not sure.