I'm very excited for all these high mpgs being reported, but urge folks to hand-calculate to confirm.
I hand verify every tank (with the added advantage of almost always using the same actual pump) and found that not only is my car's computer off, but not really by a predictable margin (or even direction). I asked my dealer about this and the responses was "You're lucky it's not off by more!"
This is my first car with an on-board mpg calculator, but my reading indicates that they're more novelty than scientific reality across the board (brands, models, etc).
I, too, have gotten 40+ mpg readings on trips -- felt like a million bucks -- until I did the math myself and saw I was still in the 34-ish ballpark.
Anyhow, don't mean to be a buzzkill, just suggesting folks consider their hand-calculated mpgs along with dashreads.