As the weak housing market and a credit crunch unsettle today's stock market, it's worth looking at the real costs of Black Monday. Consider this: If you had a strong stomach and invested $10,000 on the Tuesday after Black Monday in 1987, you'd have roughly $133,000 today. Yet even if you had terrible timing and invested $10,000 on the Friday before Black Monday, your investment would still have grown to $98,000. Now that $35,000 difference is no small potatoes. (In fact, it's an SUV.) Yet even those unlucky investors who bought big right before the crash have still earned an outstanding 12.1 percent annual rate of return versus the 13.8 percent enjoyed by those perfect market timers.