I've been evacuated from a cinema before. It was many years ago at a small local cinema, I think it was Robin Hood prince of thieves which will give you the time frame (I'm too lazy to check), There was a real incident (from my now vague memory it was something like the projector overheating) but everyone was evacuated safely and I never saw any smoke. We were let back in after a while to see the end of the film and I don't remember seeing any fire trucks turning up so it couldn't have been too serious an incident.
Mark
Mark