Metrics program are becoming very common in several areas, and more and more decision making is based on them. The idea of founding decision on numbers or evidence is appealing, though it hides several risks.
Here I collected a few quotes and pointers for further reading.
Tell me how you measure me and I will tell you how I behave.
When a measure becomes a target, it ceases to be a good measure.
The more any quantitative social indicator (or even some qualitative indicator) is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor.
Also linked is the concept of Perverse incentive.
An interesting read in the context of software engineering is:
An Appropriate Use of Metrics: http://martinfowler.com/articles/useOfMetrics.html