I'm studying neurophysiology and we are studying the effects nicotine has on your mental and physical state. I'm sure you all know about the mental side i.e. mood swings, finding it difficult to concentrate, difficulty sleeping etc. but the physical side is the interesting one.
when you have been a regular smoker for a few weeks, your body becomes used to having a constant amount of nicotine in your blood. Therefore, if the nicotine levels are dropped, your body does not know what to do. So it gives you a craving to tell you something aint right.
It takes a full three days at least for all the nicotine in your body to be flushed out in urine, sweat and feces (it is, after all, a toxin).
The interesting thing is, the lower the nicotine levels in blood, the stronger the craving.
Alcohol, believe it or not, is a cleanser of blood. it washes alot of salts, fatty acids, proteins, water and nicotine out of your system, alot of which are vital to a healthy body (hence a hangover). This is why most people crave something fatty and salty(a kebab for example) and also cigarettes after a night on the sauce.
Nicorette and patches work by supplying a small amount of nicotine to the blood. This is why these methods do not work for many people. Remember, if there is a small level of nicotine in the blood, there will be a strong craving. Using an aid to give up smoking can be comforting because you believe that you are being helped, and it works for many people. After about a week of going cold turkey, all nicotine should be out of you system and its just a psychological battle from then on.
Good luck to you all,
P.S. I stand to be corrected on any of the above points.