Google - Mars 500

While this will provide interesting insight into group dynamics on such a long trip, I don't think it will necessarily tell us how astronauts will feel and act on an actual Mars trip. On Earth, you could theoretically "get off" at any point, even if it is highly, highly discouraged. You would know, no matter what, that there is breathable air outside your simulated spacecraft. On a real Mars trip, there is no way to give up and stop the trip. I don't know whether this would be better or worse than the feeling in the simulation, but it would certainly be different.