I used to own a 2002 Nissan Xterra but I traded it in during the $4 a gallon of gasoline summer of '08 for a 1998 Acura CL. The average mpg for an Xterra is around 15.6, while the Acura should get around 24.3 (http://www.fueleconomy.gov/). I expected some pretty big savings but that didn't end up happening.
With my new car came new driving habits. The Xterra was the bare bones model, no cruise control or power anything. The Acura had everything that was available at the time of its manufacture. The Acura also could go much faster than the Xterra. I have never considered myself an aggressive driver but I noticed that I have started to become one with this car. I'm constantly in the passing lane and accelerating fast at green lights. I recently got my first speeding ticket (87 mph in a 55, not smart and definitely deserved), that along with this class has made me change my driving habits.
In my Xterra I got around 16 mpg and filled up once a week. Prior to my recent change in style, I was getting around 20 mpg in my Acura. By following the advice given on http://www.fueleconomy.gov/ I have been able to increase my fuel efficiency by 25% with an average mpg of 25. Gone are the days of accelerating just so I can catch up to the car in front of me and then apply the brakes. I no longer live in the passing lane on freeways and I take advantage of cruise control. I am also filling up less often by combining trips.
This current heat wave is hurting my mpg's. I have to blast the AC to be even close to comfortable but I am still above what I used to be getting.