Converting Story Points To Hours (That Old Chestnut)

Mike Cohn posted a very nice explanation of why it's such a challenge to turn story points, the unit of estimation used by many Agile (and some non-Agile) teams, into hours, the beloved unit of project managers the world over.  As Mike points out, it's a somewhat reasonable question when applied to a single team whose composition has been kept relatively intact over time, but a ridiculous one when applied to multiple teams, each of whom have differing ideas of what represents 1 story point of work and therefore work at differing velocities.