Aside from all the challenges that will inevitably present themselves along the way, probably the greatest obstacles are the vehicles mandated for the event. All four-wheeled machines are limited to 1 liter of displacement, while the two-wheeled contenders are allowed to max out at 125cc. The vehicles are chosen as much for their quirkiness as they are for their road going prowess and while certain modifications are allowed, heavily adapted vehicles can be subject to fines.
You can follow the progress of the teams, see the five recommended routes and check out the charities the Mongol Rally will be benefiting at their site www.mongolrally.com.
[Thanks to Christian for the tip!]