I found this fascinating quote today:
I keep hearing folks all over the place struggling with how to distill appropriate metrics from the goals they set. We’re still looking for some holy grail of turn-key metrics sets – the “accepted” ones that everyone uses. But here’s the thing: standard metrics are useless unless they specifically point to the goals YOU have set.altitudebranding.com, Breaking A Goal Into Metrics, Jan 2010
You should read the whole article.