It's remarkable how, time and time again, formal incentive compensation schemes are shown to cause more harm than benefit. I started paying attention when Joel Spolsky called it out 6-7 years ago, and then read Peopleware (an excellent book) which reiterates the point (and calls it "teamicide"), and then read the Harvard Business Review article ("Why Incentive Plans Cannot Work").
Why would a company as smart as Google forge ahead with schemes like this in the face of all available evidence that it's a bad idea?