A lot of this discussion has been regarding mental/psychological addiction and withdrawal, however few physical symptoms of withdrawal have been discussed.
In my experience I have consistently experienced the following symptoms (inclusively) whenever I have ceased smoking:

Excessive sweating/hyperhydrosis
Constipation
Insomnia
Bruxia (teeth grinding in sleep) when finally asleep
Suppression of appetite
Aversion to sweet and sugary foods

I have a number of smoker friends who have experienced some or all of these issues, and some who experience none. I do have some addictive tendencies, and tend to be anxious at times, but regardless of my mindset I do experience the same symptoms. I believe they are related to physical habituation to dehydration and increase in appetite caused by smoking.

There are pharmacological treatments, therapeutic treatment facilities and programs for those wanting to stop smoking. The designing and funding for this certainly suggests many believe marijuana is an addictive substance.

On another note, if there are ANY SUGGESTIONS AT ALL about how to reduce the unpleasantness of withdrawal, PLEASE TELL ME! I've been feeling awful since I ran out!