I once had a 1993 Lincoln that had both current MPG and cumulative MPG. It was a real eye-opener on bad driving habits. By using the current guage, I was able to get my cumulative mileage up to 22 MPG on the beast.
My trip computer cumulative MPG on the Passat has often read over 48 MPG, and sometimes over 50 MPG.  The gauge reads a bit higher than the real economy, but it's still amazing to see such numbers from a 5-passenger car.