The discount window is where banks can borrow directly from the Fed; as of today they can borrow at 4.75%, with the target for *interbank* lending @ 4.25%.
Basically, if you're a bank who needs overnight cash, and you can't get anyone to lend to you, for whatever reason, you can go to the Fed. But if you're willing to pay up 50 bps for funds, everyone figures there must be something seriously wrong with you. So the major deterrent right now is the fact that your counterparties worry about you being desperate. As a result, you're willing to pay up quite a bit in the interbank market.
If the penalty were to be reduced to 25 bps, there would be many more players much more willing to use the discount window, removing the stigma.
In other news, the previously discussed 3x2 spread didn't work today. In fact, no trade worked at all, really. Both Dec and Jan are unched. Now we get a big game of chicken in Dec.