Just how strong can a bear market rally be? The great thing about the financial markets is that there is no lack of data. You can find correlations between the temperature in Zimbabwe and the price of corn in the midwest. One thing I always found amusing was that the DAX would jump up a few points whenever Germany scored a goal in a big soccer match.
Anyway, there is an interesting comparison between this 50% run-up in 2009 and another similar bear market rally after the first part of the 1929 crash. 105 days in and a correlation of .82. You draw your own conclusions.
During 1929, after a 45% correction in the S&P 500 the market rallied 47% before continuing its slide downward to an abysmal 86% loss.