Seems like the car has to guess how much gas is in the tank and how much is being used, so the on board computer might display estimated, rather than actual calculations. Is there a general consensus as to how accurate the displayed MPG actually is?

I find that the mpg display is about 1.5 mpg on the high side. That's been consistent for me across to RX 330's and the Camry Hybrid. My actual mileage has never been higher than the display.

"When you get to the fork in the road, take it." --Yogi Berra

I have slightly more than 15,000 miles on mine and have recorded the tank computer values on each fillup as well as the recorded mileage and the gallons that I pumped. The computer is high by 1.2 mpg based on my fillups. However, when I use my Garmin GPS system I find that the actual mileage on the odometer is low. Putting this information together, I have come to the conclusion that the computer is accurate within 0.5 mpg.

Have you also verified the accuracy of the Garmin GPS system?

Yeah the displayed FE is usually high. I think I've had one tank where it was dead on or possibly slightly lower than calculated, but at the time I was more into topping off so could easily just be variation in how much I put in from one tank to the next. Now I fill till it stops, and per someone else's model, fill it till it stops a second time, then top to the next even nickel. Think that's supposed to improve the ability of the car to update the cruising range, too. Not sure it does that properly if you're overfilling.

And my info should all be on my mileage page, too, if you want to check tank to tank comparisons between MFD numbers and calculated numbers.

After 15,000 miles and checking the old fashioned way each fill up, my TCH computer tallys between .5 and 1 mpg high. The speedo reads about 3 miles per hour high and let's not discuss the miles-to-go display. Great car, it just likes to shade the truth a bit.

The cruising range will learn, at least. Though from other threads and my own experience, topping off the tank may prevent it from learning. Someone posted a picture of their cruising range showing 700+ miles I think.