It appears that banks who borrowed cheaply can actually park their cheaply borrowed dollars at the Fed--after they bought up the bonds sold by the Treasury.
Companies who borrowed from the banks in the form of "lines of credit" can turn around and issue bonds of their own, which are also bought up by the banks--with the cheaply borrowed money from the Fed. And the companies that borrowed from the banks also turned around and picked up a few juicy corporate bonds from other companies that pay a slightly higher interest rate.
And everybody who "invested" decided it was safest to park their dollars right back at the Fed! What's not to like? Everybody who bleached their brain cells as much as I have before heading out to have them pickled by a Cosmo at Ramsi's is over the moon with delight!