So far, I have only had it off when I want to get the rear end squirrly in the snow...LOL! Generally speaking though, I leave it on as it is a safety device. If you find yourself in an emergency situation how likely is it that you will be able, or even remember to hit the button to turn it back on? Wtih the ice that we have had around here recently (30 car pileup Arnprior Thursday, 50+ car pileup Montreal Thursday, and another multi-car pileup Ottawa-area Friday), I am not touching anything. I can live with the gas mileage I'm currently getting (~400km/tank, mixed city-highway driving).
R