They certainly removed the register link from the header bar and at some point announced that to keep server costs in check, registrations would be closed. I don't know if you can successfully submit a registration when opening that address directly but considering that the admins don't want additional users for understandable reasons, I'm not going to try what happens.
Edit: Oh the register link is there under the login window. Seems they reversed their decision, maybe after enough donations arrived. Very good.