Chart 1 gives the composition. You can see that QE1 and QE2 were mainly bond purchases (light brown area). QE3 should be another round of bond purchases and should expand the light brown area again.
Second, the spike in 2008 was mainly lending to financial institutions at the time of the banking collapse. This lending has been paid off in 2010.
But the most interesting part is the mortgage backed securities area in brown. In that period, congress passed the Emergency Economic Stabilization Act of 2008, which authorized the Treasury to purchase mortgage-backed securities. As a consequence, the brown area increased in size at the same time when lending to financials decreased. That means that the federal reserve has bought approximately $US 1 trillion of mortgage backed securities in an attempt to support the housing market. It didn't do much to the housing market. New home sales and housing starts were flat, but the housing market index improved a bit though.
I will point out the importance of convexity to make my case of lower interest rates in the foreseeable future.
|Chart 1: Federal Reserve Balance Sheet|
To read the analysis go here.