I quit smoking about one week ago. My story is a bit strange because I had quit twice already in my life, always cold turkey. And both times I started again because hanging out with smokers and partying hard.
The first time, I had quit for three years. The second, for five years or so. Of course I agree with all the other have said so far, and because I do not really enjoy cigarettes, I think I have quite for good now.
One thing, if you party hard, and like to smoke 'something else' from time to time, pay attention, because these have been the factors that lead me to start again, twice.