There's a Forbes article about how many new car buyers -- not just hybrid purchasers -- have been complaining that they're not seeing the EPA's MPG ratings in real-world driving conditions. Apparently, the EPA is considering revising the way they calculate MPG for new vehicles: Personally, I agree with the end of the article:
You can comment on this proposed new change to the EPA's testing procedures here for the "Petition to Amend Fuel Economy Testing and Calculation Procedures; Request for Comments" until 7/24/2004.