I don't allow smoking in my flights too, the no smoking sign is always on because it is a matter of safety, and respect of non-smokers.
However I am a smoker myself and during flights (especially long ones) I always feel the need to smoke and I would like something to be done about it. I mean, it's ok to respect the ones that don't smoke, but what about the others who smoke? It is terrible to want to smoke during a long trip and to know that there are still 5 or 6 hours till landing

What about Euroharmony be the first airline company to introduce smokers and non'smokers seats?
Another option whould be to have some special places inside the plane (eg. toilets) with the appropriate modification in the ventilation systems that will not allow the smoke to be spead?
What do you think?