Comment: An *additional* metric, not a replacement (Score 1) 182
There is no measure of productivity that does not have huge flaws. We'd like to measure quality but there isn't even a reliable definition of quality.
Other posters have mentioned that developers will game the system. That is true. Even if the metric is simply personal observation, people will exceptional and sometimes devious social skills will game the system. That is what office politics and the good old boy network are about.
If trick is to combine subjective and object metrics (even if flawed). You need the objective metrics to catch the social slackers. You need subjective measurements to catch deliberate distortions and account for variations in working styles.
Granted, there will always be idiots who will a tool inappropriately but that does not mean it is a bad tool.