I quit Jan 4th this year (it was the first monday of the year) and joined a gym 3 weeks later because it had a promotion thing on.
The first 3 months were a killer, I didn't tell any friends to begin with but had to tell my boss incase she noticed any drastic behavioural changes. I apologised in advance for the nasties to come, they didn't. My friends sussed it out after a few hours, usually I spark up straight away.
After that the health benefits kicked in, less breathless, more energy, food tasted great, didn't smell like an ashtray. People even commented that my smokers cough had gone after the initial batch of coughs cos the lungs are a bit afraid of fresh air
Dooms day I caught a chest infection from someone at work because she was answering everyones phones if they weren't there, we told her not to. My smokers cough came back with vengence I got a telling off cause they thought I was smoking again. The cough went on for months I did go to the Docs and asked about the big 'C' but no lungs sounded all clear, the cough is gradually getting better.
My advice for all who has began the quitting process or is thinking about it start on the multivitamins or at least Vitamin C get your immune system up to scratch cos a cold, flu or any respiratory virus can take ages to get rid off.
I'm at the end of my 8th month YEY! and my 4th try, I still miss the motion of smoking but have come too far to go back now and it a VERY expensive habit