Mariokart Wii definitely gets the addicting award. Holy crap, I played that for so many hours. Whenever my friends and I played, I had to try to remember to 'forget' a lot of my tricks so as to not be a complete jerk while playing, lol. I think I placed pretty highly in one of the competition thingymajiggs - I can't remember which one, though. It was probably a year or more ago by now.
I don't have to do that, my main opponent is my brother-in-law, and he's a pretty good Standard Kart drifter.