Quote from ScalperJoe:
There could be several reasons why the announcement was bullish for stocks, to name just a few:
1. Declining yields on the 10-year treasury after the fed announced they would keep interest rates next to zero until mid-2013, and no indication of more "QE" nonsense (thus far).
2. The fed announcement was met by the usual violent whipsaw action until the S&P found support around 1,100 (the November 2010 low). Longs started buying in droves, and/or shorts covered.
Whether or not the "very bullish reversal" is the true bottom is anyone's guess.