My reasons for quitting are the same as many I suspect, but I think they are the best possible reasons.
My partner and I had a son just over 2 years ago, she stopped as soon as she found out she was pregnant. Just stopped. Just like that. I was so proud of her. I tried to do the same thing and failed miserably. So I just stopped smoking in the house and in the car.
2 Years later (son aged around 15 months) I started trying again, tried just about every NRT method available and it was either they didn't work for me or I was just halfhearted about it (I suspect the latter) but I failed over and over again.
Then I realised that I was concentrating on the wrong bit. My Dad died when I was 13 - a year after I started smoking - from smoking related stuff. My Mum has been very ill from smoking related stuff, and if she dies my son will have no grandparents on my side of the family (My partner is Polish - so his nearest grandparent will be thousands of miles away!). That's not good. But worse than that, I had to go through my teens with no father - I will not let that happen to my son if I can do anything about it. So there. And I want to see him grow up and have children.
So there we go. I decided to get serious a fortnight ago. I went to an advisor who prescribed Champix and have now nearly made my first week smoke free. I will never smoke again - "not even 1 puff". It's in writing now, theres no going back.