An idea that has decent face value and is tested by very few; the two hallmarks of a wide-spread urban legend.
In the U.S., there are an estimated 900,000 elevators, each serving an average of 20,000 people per year. Collectively, U.S. elevators make 18 billion passenger trips per year. Those trips result in about 27 deaths annually, according to estimates from the U.S. Bureau of Labor Statistics and the Consumer Product Safety Commission.
Even among these, very few are results of free-falling elevators. This is because they are held in place by 4 (or sometimes 8) cables, of which even 1 could hold the elevator. Even if all the cables were cut somehow, an automated emergency brake system would step in and stop the fall.
However, with a free-falling elevator the jumping method wouldn’t help, even if you managed to jump just before impact (which in itself should be extremely difficult, as you don’t see the ground). Jumping would only change our relative positions to the bottom of the elevator and you’d hit the ground at the same speed as the elevator does.
How Stuff Works recommends that if you find yourself in a free-falling elevator, you lie down. By doing this you stabilize yourself and spread the forces that act on your body upon impact (don’t expect this to be pain-free though!).