I quit for 2 months last year. In just two months I had seen major improvements in general health, capability to just do random things and not get exhausted (house work and shit), my performance in all areas related to training went up big time, etc..
However, I thought I could control my habit and decided to have one every week or so. Eventually I was back on after 3 months of being off. Dumb decision, and I'm still smoking now. Every weekend I say I'll quit, and I never do it.
So if you've made it a week, you can most certainly do it. Don't be a fucking retard like I was.