Allen Holub believes in #noestimates.
In his blog post KPIs, Velocity, and Other Destructive Metrics he offers this alternative to useless metrics tracking:
Focus on continuous process improvement, and productivity takes care of itself.
He has this to say about Velocity as a useful measurement of productivity:
velocity (average points per sprint) is not a performance metric, and using it as such is actively destructive. For one thing, the basic unit (a point) is not a measurable quantity. It’s a judgment. You can’t derive a quantitative measure from qualitative input.