An allegedly true story about unintended consequences:
I worked as an accountant in a paper mill where my boss decided that it would improve motivation to split a bonus between the two shifts based on what percentage of the total production each one accomplished.
The workers quickly realized that it was easier to sabotage the next shift than to make more paper. Coworkers put glue in locks, loosened nuts on equipment so it would fall apart, you name it. The bonus scheme was abandoned after about ten days, to avoid all-out civil war.
This was from Scott Adam's Dilbert Newsletter #44, so you might want to take it with a grain of salt.