The societal and environmental benefits of plug-in electric vehicles (PEVs) have been well documented. However, the near-term impact of PEVs on the distribution grid has yet to be fully explored. Whether PEVs will help or hinder electricity provision will depend on how customers charge their vehicles, which will be driven in part by the rate structures that are offered by utilities and the associated customer response. In this discussion paper, we explore the relationship between PEV charging behavior and varying time-of-use rates, and offer suggestions for conducting a well-designed pricing experiment that will determine whether varying rates will help reduce future grid reliability problems as PEVs penetrate the vehicle market.