Quote from: bizz on December 10, 2013, 09:54:30 PM

That might be a problem for offline or paper wallet creation. Something I would like to see in future. Since when offline it can't be known if an account already exists.

Yes, but one can work around it. All that has to be done is the public key of the account needs to be announced to the network somehow. You can sign a transaction (send 1Nxt to yourself) on an air-gapped computer, then broadcast it to the network using a connected computer. Or a special transaction type could be created, which purpose is just to announce the public key of the account, with zero amount of money moving and no fee.
When you try to broadcast that transaction to the network, you will get an error if the account already exist. Then you just need to try again, generate a new account number offline. It is extremely unlikely though - unless you used a common password and not a randomly generated one.