News reports about a recent isolation experiment designed to assist in evaluating the effect of a voyage to Mars can be found here and here. The six male members of the “crew” were kept isolated in cramped quarters in a Moscow suburb for 105 days, and the project tried to simulate other aspects of a mission to Mars, such as a 20-minute delay in communications with Earth, occasional emergencies, and so forth. The experiment is the precursor to an isolation experiment lasting 520 days — the approximate length of a trip to Mars — that is to occur in 2010.
I think the value of the experiment is limited, because the crew members did not have to deal with zero gravity, apparently ate normal food, and understood that they could leave the isolation chamber in the event of an emergency. No matter how realistic the simulation was, crew members must have realized, deep down, that they were really in a Moscow suburb rather than hurtling toward Olympus Mons. As a result, some of the mental and physical stresses of a long space voyage were not, and could not be, realistically simulated. Nevertheless, I think it is encouraging that at least some space agencies are looking forward to the days of extended space travel, including visits to our neighbor The Red Planet.