|Source: New York Times|
As shown, there have been 3 instances of 4 consecutive days where the average moved by more than 4%. A 4% move today is even more interesting when you consider that savings accounts offer less than 1%.
With the DJIA at 11,143, the math works out today to be a bit over 100 points for each percent. The 1987 20% drop is the infamous "'87 crash" that is constantly referenced.