Dustin Moskovitz co-founder of Facebook stated in his interview at Disrupt San Francisco, "You get what you measure". I think this is important, because what you decide to measure is what as a result you will continue to modify and change- in order to impact the measurements. So whatever metrics you focus on will be the result of what you are desiring.
It reminds me of another similar quote, "When performance is measured, performance improves. When performance is measured and reported back, the rate of improvement accelerates".
So choose important metrics. Identify what you want and begin to measure them.