Smoking or Non-Smoking?

In the same thread as the "Must Love Dogs" post,
I'm now looking at the subject of personal controlled combustion,
smoking, that is. 

From the very first time that European sailors stepped ashore in North America and saw one of the locals burning tobacco and breathing it in,
we've been asking ourselves and each other "smoking or non-smoking?"
Since the 15th Century, we've been asking that question.

At first it was "Why?", then "How?",
followed by "Where can I get these big leaves?"
Next probably came "Oh, the folks at home are gonna love this."
Eventually came "Hey, umm, turns out this isn't very good for you",
and finally "Uh, guys, you think you could maybe do that somewhere else?"

When someone asks you "can we smoke on your gondola?", it's important to remember that they are essentially asking "would you mind if we set something on fire aboard your wooden vessel?" 
There aren't as many smokers today as there were twenty years ago, but we still get the requests.
Say "no" and you could effectively ruin the experience for your passengers.
Say "yes" in just the right way, and you may just bring their gondola experience up a notch for them.
As with many potentially awkward situations, I like to answer in a way that's funny, but also gets the point across - something like "No problem, just remember that the thing we're all floating on is made of wood; set it on fire and sooner or later we're gonna run out of places to stand".

Having a ready ashtray can mean the difference for your passengers.

Of course before allowing someone to smoke on your boat, it's important to determine what exactly they'll be smoking on board.  The laws regarding the smoking of marijuana have been changing quite a bit lately, but I'm not sure if the Coast Guard shares the same progressive opinions.

So what do you think?
Do you allow smoking on your boat?
What are the pros and cons according to your experiences?