On the Magic, Off Beat is non-smoking all the time. At Sessions, you can only smoke at the bar, the seating area is non-smoking. I never notice smoke when sitting at one of the window seats. Rockin' Bar D allegedly has a non-smoking section, but I couldn't tell where it was. It does get pretty smoky in there at times. The Promenade Lounge and Studio Sea are both non-smoking. ESPN Sky Box allows smoking, but It never really seemed very smoky in there.
It's a tough call for the cruise lines, I think. I'm sure they'll consider many different plans, and there will always be a group of people for whom it doesn't work. People do smoke, especially when they drink. I guess I'm lucky it doesn't bother me that much, although it does bother me a bit more since they've banned smoking in restaurants and bars in California. I guess I'm losing my tolerance....
Carnival has a smoke-free ship, I think it's called the Paradise. Apparently they'll charge you for a first offense, something like $150, and actually put you off the ship for a second offense.