Excellent question. The short answer is yes. Laughing implies happiness and low stress. There have been many studies trying to understand the effects of emotional stress on the body and it is clear that stress can have significant physical and psychological effects. Numerous physical ailments can be exacerbated by or even caused by stress, such as headaches, nausea, muscle cramps, suppressed immune system, high blood pressure, eyesight problems, etc. Stress can also make people less likely to take care of themselves - for example not sleeping enough, not eating right, not exercising, ignoring health problems, making risky decisions like starting to smoke cigarettes, etc. I think it is safe to say that in general, the less emotional stress a person has, the less physical stress is put on their body (directly and indirectly), which can be correlated to living longer. So, laugh often, be content with what life gives you, and pass on a smile to the people around you :o)

Maybe - it lowers stress, blood pressure, etc., all of which can lead to an early death. If you will die because of a stress and reactions to stress, then laughing will help you live longer. If you will die for some entirely different reason, then laughing wouldn't affect your lifespan.