Most folks I know who have stopped smoking have gained weight - but I think it has more to do with not breaking the hand to mouth habit than anything else.
I rarely bother with cigarettes if I'm curled up with a good book - but can wipe out a can of peanuts or a bag of chips without even realizing it.
Of course I can get away with that - I'm 5'10" and 115 pounds :)
Holy moly you are tiny! I picked up the habit in college and had to quit and you are right. I started carrying a pencil around to keep my fingers busy. My father in law wipes out cans of peanuts and doesn't smoke! LOL! He is one of the people that bugs me when it comes to his fatness. He consumes a HUGE amount of food and alcohol and then blames it on genetics. He talks about how his mom was overweight. He forgets that when they lived in Germany and left in the 50's, none of them were overweight. Selective memory, I guess.
The trick to that is not to sit down with a container of snack foods, but to serve yourself out a reasonable portion. When I'm having some nuts or even potato chips (I try not to eat those too often, although the vending machine 50 ft away from my cubicle is a constant temptation, LOL), I get a bowl - a small pyrex glass bowl for nuts, a smallish pottery bowl for chips - and dole myself out a reasonable portion. If I go back for more, it is a concious decision.
I've porked up a bit in the last couple of years, and I think it has to do letting myself indulge my taste for fast food a little too often. Also the lack of activity for a couple of months this winter after I broke my collarbone skiing.