I find it interesting that they chose Cary, NC for this pilot project. I am not aware of any programs that encourage electric cars in NC nor am I aware of large enough numbers of electric cars in the state. I know there are several states that offer incentives but I am not aware of any in NC (beyond the Federal tax credit that Tesla is using to get the Model S below $50k.
You do have to start somewhere with charging stations. Even if you only stay 20 minutes you can still get a significant charge. 20 minutes is an easy to hit timeframe. You plug in, walk in, wash your hands, line up, place your order, wait for the order, sit down to eat and then walk back out to the car.
For those who are saying you will have to stay for hours you are thinking of the max charge time. Yes if you pull into this restaurant with little or no charge left and try to get back to a full charge you will need a lot more time. However if you pull in with half a charge a 20-30 minute stop will be enough to bring you up to at least 60% (consider that the Roadster on a 240V/70A charging circuit should need 3.5 hours to go from 0-100%).
If the charging stations become commonplace then everywhere you stop you'll be able to get yourself at least a 10 minute charge. Suddenly electric vehicles with "short" ranges could take you through a full day of errands around town. Each of the charging stations would give you that extra little boost to keep the car going all day and then you simply top it up at night.
As for the source of the power - yes green sources are better, but even a dirty coal plant and transmission losses offer better efficiency and lower pollution than using thousands of gasoline powered engines as small generators.