I've registered and gone back to finish the registration, getting the "You are now logged in and can update placenames," message, but I still can't access the api with my own credentials. I still get the "user does not exists" error message when including my username in the url of a search. The demo account works, other than already having used up its credits for the day.
We had some performance issues due to overload and had to change the config two days ago. This means at the moment it takes longer for all server to sync new accounts.
I think your account should now be visible on all servers.
I am sorry for the inconvenience.