If FBI did issue a gag order against Gox as rumored, a lawsuit will get you nowhere.
But it's worth trying at least
But it might be just a waste of time, and you need to pay for lawyers etc..
And result will be : that you will have to wait for your
BTC anyway - same shit...
I think people who want to sue him now should wait a little bit longer to let things settle...
Maybe there will be no need to sue them.
And later, if they will start withdraws again you can sue them for what they did to you and to your mental health

