230 MPG or Whatever
Without other energy input there is no way a Chevy Volt will be able to go 230 miles on one gallon of gasoline. I've gone into detail about this before here.
These types of claims are damaging to the nascent EV and hybrid vehicle industry. There's already too much hype and vaporware out there, the last thing that's needed is for a major company and the government to exacerbate the situation.
This is a prime example of regulations lagging technology. A clear way of defining energy efficiency for vehicles that don't run exclusively on liquid fuel has not been established by EPA. There's also the specter of government ownership in the company (GM) leading to self-serving circumstances.