There is a slight reduction in the bill; somewhere around $9/month on mine. There appears to be no downside to staying in since the program will likely be renegotiated next year and there will be another opportunity to opt-out.
Meanwhile, has anyone wondered how much extra we pay in our bills for the foolish waste of money that National Grid (for example) has to pay out for sending us our "energy scorecards" every month or so??????????????