It seems like the biggest business story of the past month has been the insane success of General Motors’ “employee discount” program, wherein customers get the same price for cars that GM employees get. The question I’ve been wondering about is how big a discount customers are really getting. Reading the paper this morning, I learned the answer — customers paid $400 to $500 less for GM cars in June than they did in May. Obviously the words “employee discount” are magical, because the raw savings certainly can’t account for the sales growth GM has seen. The program is scheduled to end on Tuesday but GM is considering extending it, and Chrysler is going to offer an employee discount sale of its own. I can already see the magic fading away.