I am on my 4th tank now, but on my third tank of gas, I got 19 miles per gallon, up from 16 in my first two tanks. The only change I made was the decision to always drive in M-Mode, and I still took it towards my 5500 RPM limit a few times. I have already seen (I reset consumption with every tank) times early in the tank with freeway driving @ 75mph at 22+. I've actually had the opposite experience as lugnut with dash readouts using the reset consumption on fillup. In the M3, my previous Audi A4 and our Lexus GX -- they all seem to be fairly spot on.