I did a quick Google search and came up with many links with TOO much information... but figured you have done that also. So, I thought I would throw in my physical experience, which isnt opinion. I have smoked for 17 (started at 14) years and quite twice. Both times, the reason I "re-started" was because I thought I could be a social smoker- smoke when out for a beer or during other certain activities (I know, only deluding myself). Both times, for a wile, I could handle that- but both times, I soon began smoking regularly again.
I cant comment conclusively about the health implications of "a cigerette a day" or only "socially," I also dont think there is sound statistical proof one way or another concerning this type of behavior- what you are requesting... it would be almost impossible to qualify because of so many other environmental factors. But, I think one could safely infer the effects based on already established statistical information regarding normal cigerette/tobacco use and its physical effects (but would this be opinion?).
However, I do think it is its own gateway when done socially.
Dont know if I really helped at all here.
EDIT: hehe... figured this was about you, Surreal... you share my delusions?