Just so you know, the course is built of concrete with chilling tubes containing ammonia in the concrete. By varying the amount of refrigeration at various points on the course, the operators can subtly alter the track conditions to increase friction at various points on the course, thereby slowing the sleds.
In addition, they have raised the retaining wall at that part of the course and shortened it by changing the start points for the sleds; http://www.comcast.net/articles/news-general/20100214/OLY.Olympic.Rdp/
Competition began on a repaired, reconfigured track the day after Georgian luger Nodar Kumaritashvili died in a crash during a training run.
The men were pushed up 600 feet to the women's start ramp, while women and doubles moved 800 feet to the junior start ramp.
The changes produced slower speeds, as intended. They also drew some backlash, with the Canadians saying they lost their home-ice advantage and a top American luge official saying, "The elite deserve to race from the hardest test."
Is there something so wrong with some people that they can't accept the fact that the designers of the Whistler Mountain course made it too fast and too dangerous, IMO?
As for nets: If you have in mind something along the lines of the catch fences used at racetracks to keep cars from going into the stands, I honestly doubt that would work, as they would only fling a slider - a person - back down onto the ice.
Perhaps a net barrier like those found at airports and on aircraft carriers, which give on contact and gradually slow a runaway plane to a stop might work. They'll have to look at all of this, just as auto racing has done in recent years, now that the technology of speed has outstripped the technology of safety.