You get 14 miles of electric MPG boost, from plugging it in for 3 hours to a 110-volt outlet.
I accelerated just like I normally do with my 2010 Prius, uphill through the suburbs and up the ramp onto the highway. Notice how the engine stayed off until reaching 50 MPH, at that point the power demand from the acceleration caused it to start. Once on the highway, you can cruise up to 62 MPH without needing the engine (0 RPM). Faster than that, you'll see much more electric-motor activity and reduced engine use than with a no-plug model. The efficiency benefit from the plug is quite impressive.
