The Standard & Poor’s 500 stock index is priced at about 21 times forward earnings estimates by Wall Street analysts -- a high P/E multiple by historic standards -- but not as high as the peak of the stock-price bubble in 2000, when the price-to-earnings ratio of the S&P 500 peaked at 25. Moreover, things really are different this time. Bond yields are near a historic low, making the earnings yield of stocks a relatively attractive inve..