As of August 15, the Earth-bound astronauts were in isolation for 438 days, beating the "real" record holder who actually spent more than 437 days in space during one trip and 240 days in another. Polyakov spent a total over just over 678 days in space as a cosmonaut, but that was more than a decade ago. The ESA experiment hopes to gain data of isolation on the ground that they can more easily monitor.
The astronauts are living out their long stay in a small facility of 550 cubic meters (around 1800 cubic feet) located in a Moscow parking lot. It contains limited amenities, beds, a kitchen, a greenhouse, and a couple other facilities. The group also receives limited contact with their loved ones to simulate real space-flight (communications delays between 8 and 736 seconds depending on their distance from Earth).
During their "trip" to Mars, the group "landed" and walked on a fake Martian surface, conducted scientific experiments, exercised daily, and did other activities that astronauts would actually do in space to keep themselves occupied. They are currently on their mock return trip to Earth, and have about 81 days left as of this writing.
This long-term isolation experiment will help scientists evaluate what astronauts are capable of handling and help them design long-term space missions. They will "land" on November 5, 2011, totalling 520 days in isolation. Let's hope they don't go insane before then.