I actually thought they turned themselves off a couple of years back — one website I use started failing because their login was handled by a separate domain.
I never bothered to turn off anything myself though. I've made my peace with websites having ads to survive, and if I'm going to see ads it might as well be ads that are relevant to me. My life is so boring that I'd be flattered if anybody was interested in my secrets.
Biting the hand that feeds IT
