Guys -
Before you get tricked by the headline 9T number, use your heads instead of taking this as something it's not. A lot of overnight loans are the same loan rolled over for many days, even weeks, each roll-over being counted as a separate loan. So sorry, it's not really 9T unique dollars. That's like saying there are 50 billion people on earth because that's how many people have been born throughout history.
Also keep in mind that banks that didn't need these loans took them because they were such a great deal. Shit, if I could get a 0.5% loan fora few billion to leverage against I'd do it too.
"Fuck you KK - get to the point.."
My point is is that a few large banks fucked up bad enough, and had enough leverage and counter-parties, to warrant the Fed stepping in with the discount window changes, and since they couldn't just let the "bad" banks have the access, everyone did, and took advantage.