>There's such mail, since the account is not even created until one
>confirm it with an url given in the mail.

But that message doesn't contain the username.

When you register as a new user you get a message asking you to click on a link to complete registration. But there is no confirmation message saying 'yes, you have registered and your username is X'. I think it's important to send such a message so the user can save it in a mail folder somewhere - most websites with registration do this. In my experience forgetting a username is much more common than forgetting the password, and harder to recover from. So a reminder of the username you chose would be very useful.