Don't know if this has been suggested already, but I just had the idea of linking Kiva with a quit-smoking scheme.
Instead of putting the money you don't spend on smokes in a piggy bank as a motivation, you lend it to some entrepreneurs and every week you add a new face of someone else who has benefited from your decision to your portfolio - you could look at them as your growing personal support crowd cheering you on to get through it.
While the indefinite challenge of never smoking again may appear too abstract and daunting, you could just set yourself the goal to stay clean until the first loan gets paid back in full. You get to watch its progress as the installments come in and by that time, you should be over the worst and can reassess.
Added benefits would be that looking through the entrepreneur pages gives you something else to think about while you are craving and you will be less likely to feel too sorry for yourself when things get a bit tough.
I'd love to try it, but I gave up smoking years ago.

I reckon there could be some merit in it, if it was presented properly - maybe in partnership with some health/self-help/anti-addiction entities. What do you guys think?