As an energy consultant with Navigant Consulting, I use my IEOR degree almost every day.  A recent project involved risk analysis of deferring transmission and distribution network upgrades with a utility's targeted demand-side management program.  I ran Monte Carlo simulations to determine the likely range of capacity deficit or excess in congested networks after deploying energy efficiency measures.

I'm a 1964 UC-Berkeley engineering grad with an IEOR major, and since graduation my professional life has followed a path that I never could have predicted but that in retrospect seems to make sense (sort of).