The owner of that site needs to shut it down. This kind of thing was inevitable and we warned about it from the start. Someone has calculated a rainbow table and the passphrase you chose is in it.
Which wallet software did you import the key into? Do we need to put a warning about this site into wallet apps? We need to find some way to kill this stupid and dangerous site asap.
over-react much? of course someone has made rainbow tables, so what? the lesson to be learned here is not that we should crucify brainwallet.org, it is that we should make strong passphrases.