I'm working on quitting too. I smoked for 6 years, and then quit for about 8 months, and then I started smoking while I drank, and then after meals, and then in the morning, and then I was all the way back in it. But not for long- only about 2 months this time. Eating and drinking are my biggest triggers, and it's not quite feasible to avoid them!
But, like other people, the biggest incentive was my riding. After I started smoking again I just got much, much slower, and I got much more winded. Now I've cut down to maybe one a day, and that will go soon too. Cold turkey is just unnecessary pain for me. But I already feel faster, and it won't be long before I'm back to my pre-relapse fit self.
We're lucky that we have such an obvious negative impact staring us in the face- being slower on our bikes- to make us quit. The real dangers- like lung cancer and obesity- are less proximal, and so easier to ignore.