I'd like to see pipe smoking as it seems like something I'd expect a dwarf or a human to enjoy. Oh and remember it "wasn't" unhealthy back then, or so they said.
You say recreational drugs, not all drug use is strictly recreational. What about drugs used in rituals? Its certainly not unheard of for a tribal society to use certain vision inducing plants to get them closer to their gods. I think it would be a nice addition to religion in the future.
Oh and certain drugs used as medication also makes sense if Toady decides to flesh out medication in that way, after all legal medication and illegal drugs are pretty much the same thing in that when consumed they alter biological function.
As I recall, there's some sort of chemical (and growing process) that American tobacco farmers add/do to tobacco plants, that's supposed to make them "taste better", and as I understand it, it may be that (the chemical, the process, or a combination of the two), that actually makes tobacco unhealthy, or atleast considerably more unhealthy than it otherwise would be.
Also, smoking tobacco from a waterpipe (hookah) is supposed to sharply reduce the amount of tobacco toxins, as is heating the tobacco beyond a certain temperature.
Not that I'm encouraging anyone to smoke, but I do encourage taking the time to do some research into healthy/more healthy methods, if you're going to do it anyway. If a few hours of research can give you 20 more years of life (in which to smoke), then it might be worth your time?
And, for that matter, our dwarfs might enjoy the occasional hookah. That'd be a fun item to use glass for.