According to Alan Blinder, writing in the Wall Street Journal, the Fed’s latest operation includes a detail (“the sleeper in the package”) that is aimed at boosting the housing market:

For more than a year now, the Fed has been allowing its portfolio of agency debt (e.g., Fannie Mae and Freddie Mac) and mortgage-backed securities (MBS) to shrink naturally as mortgages are paid off and securities mature. To maintain the size of its balance sheet, the Fed has been reinvesting the proceeds in Treasurys. But starting “now” (the Fed’s word), and continuing indefinitely, those proceeds will be reinvested in agency bonds and MBS instead. The objective here is exactly what it was for the first round of quantitative easing, QE1: to reduce spreads between MBS and Treasurys (which had widened a bit), and thereby to help the ailing housing market.