When we complain about metrics, it seems that we focus on the potential for abuse. A team that will optimize whatever measure that is put into place. A consultant that considers yak-shaving as billable, even if that means their projects experience an overrun.
But what about metrics when the environment is a high-trust environment?
What if the team truly wanted to improve and their management truly wanted them to improve, and their clients were bought in as well? If the potential for abuse is eliminated (or low likelihood) then why not use simple, non-invasive measures to rally around? Why not celebrate that .5d-improvement in cycle time?
Work on trust first, then metrics.