In a bit of tongue-in-cheek marketing, GM blog has posted a video showing the dash display of a Chevy Volt leased by General Motors Battery Systems Engineer Andy Oury.
Showing the Volt's maintenance mode, which cycle the fuel and lubricate parts of the vehicle if the engine hasn't been used, the dash display also shows the vehicles lifetime MPG numbers of 1554.1 Miles range having used just 0.5 Gallons of gasoline. This is a good illustration of the main advantage of a plug-in as opposed to a non-plug-in hybrid electric vehicle.
Note: The 2011 Chevy Volt has an EPA-estimated 35 miles on a single charge; EPA-est. 93 MPGe [electric]; 35 city, 40 MPG hwy [gas]. Actual range varies with conditions.