With very few exceptions, there are designated smoking areas on most ships. I don't believe there is smoking allowed in the dining room or in the theatre on any of the ships, but there are always enough lounges where smoking is allowed so that you can enjoy the entertainment. When we sailed on Spirit we had no problem finding an area to smoke.
They allow smoking on one side of the ship on the weather decks. (those arteas that are outside. In addition they usually have one side of most lounges that are designated smoking and the casino. They no longer allow you to walk the Promanade or hallways smoking.