In 2002, Ben Bernanke gave a now-famous speech outlining the Federal Reserve's options if the economy ever faced an imploding economy even while the short-term interest rates it traditionally uses for economic stabilisation hit the "zero-bound". This zero-bound is a problem, because the Fed can't set negative interest rates – people can always just switch to cash if interest rates go negative.
There are, of course, other policy levers besides short-term interest rates. The $790bn stimulus package is a rather prominent, and conventional, example.
However, in his 2002 speech Bernanke identified some decidedly non-conventional levers to argue that even the Fed still has ammunition when short-term rates run up against zero. Specifically, the Fed can target long-term rates by buying long-term Treasuries and "agency" bonds issued by Fannie Mae and Freddie Mac. With luck, this would drive down other long-term rates throughout the economy and spur business and consumer spending.
In short, it's one more clever way to obscure the ongoing socialisation of banking sector risks (but not profits). By now, many Americans are tired of the "fix the banks first" strategy that TALF (and more famous acronyms like TARP) represents. They thought that trickle-down economics was gone for good.
http://www.guardian.co.uk/commentisfree/cifamerica/2009/mar/19/federal-reserve-quantitative-easing