Most of the money the Fed printed during QE 1 & 2 has not entered the economy. This is because banks are holding the new cash in the form of excess reserves, and receiving interest from the Fed. In the past, interest wasn’t paid on excess reserves, so this is a completely new tool introduced by Bernanke. Anyway, we’ll have to watch whether QE 3 ends up in excess reserves, or makes it out into the economy. The Fed could also lower the interest rate on excess reserves, which would incentivize banks to lend. My take is that at some point all of this money will flood the system and lead to some pretty significant inflation.