There is a message on the site - once you log in it really stands out and points to this forums thread. I've also halted all trading, so no one will sell Bitcoins he can't withdraw. Trying to make an offer will also take you to this thread.
If I were you, I would get it back up asap, but with a minimum trading fee.
At least this way you can start filling up the pit, bit(cent) by bit(cent).