The premise is pretty simple - men race while carrying women through an obstacle course. Numerous different carries are allowed: piggyback, fireman's carry, or the preferred Estonia-style (pictured above). Major competitions are also held in Wisconsin and Michigan. The North American Championships take place every Columbus Day weekend in Maine.
More information can be found at the World Championship's official website, to include past results, rules, pictures AND the registration form for 2008's competition. Also check out Wiki for a little history lesson.
The LOML and I are already training for next year's event. Why you ask? First prize is the wife's weight in beer!