I use the web site www.mymilemarker.com to track all of my fuel purchases. This site allows me to use twitter to log my mileage, gallons purchased and cost per gallon with a SMS message every time I fill up.
The 2008 Lexus RX400h hybrid is rated at 24 mpg on the highway and 26 mpg in the city. Over the last two months plus I have driven 4,016 miles and averaged 25.1 miles per gallon. The mileage per tank has generally ranged from a low of 24.5 to a high of 26.8 miles per gallon. I had one tank below 24.5 mpg (20.3 mpg); this was on the way up to Chester with the bikes on roof rack. In two months, I calculate that I have saved more than $360 in fuel costs than if I was driving the Explorer.
I continue to be very pleased with the vehicle. In particular, the bluetooth and iPod integration work extremely well. Although the feel of the electric motors to brake the car takes some getting use to (Sharon complained about it the one day she drove it), I am happy with the way it drives. The one omission that I find odd is the lack of a range indicator; I am used to have an indicator that tells you how much farther you can go on the current tank of gas.