(was originally part of "I don't like smoking, but I like smokers
I don't smoke, but it's true that smokers are among the most outgoing & friendly people around. There's several reasons for this:
a) On a most basic level, smokers often run out of matches/lighter fluid etc, and this involves going up to another individual (often a stranger) and asking for a light. Doing this week in, week out, over the long term can only lead to a more confident technique in approaching strangers.
b) Following on from (a), asking for a light will often spark a conversation between the two individuals (or depending where you are, maybe more). Their common ground is the strong attachment they have towards smoking; if they're both smoking at the time, they'll also feel more relaxed and be able to converse more easily.
c) In offices over the world, smokers are forced to stand outside the doors. Standing out there alone is lonely, and generally smokers will get to know more people purely because of the necessity of having to ask if they'd like to come outside for a smoke. Once outside, conversation is also made much more freely than inside.
d) In desperate circumstances, between friends, or sometimes just at random, smokers are going to have to ask other smokers for a cigarette. I've talked to friends who smoke(d), and every day, people approach them or they approach others to bum a smoke. Since the illusion is created of individual cigarettes being cheap, there's no real problem in taking/giving a couple of cigarettes, and yet again, gratitude and/or praise needs to be given/received.
There are probably other reasons too, but I believe that all the above situations, repeated over time, generate & improve character traits such as the sense of humour, interesting opinions, life & soul of the party, etc etc mentioned above.
And finally of course, you never hear smokers bitching about non-smokers.