I was advised to post it here.
Here is the e-mail which I've received from the blog:
As you can see, it's using the username/ID.
I've checked at my profile at: http://cstheory.blogoverflow.com/wp-admin/profile.php and my nickname was different, so I've tried to change the username, but it reads:
Username: 22370; Usernames cannot be changed.
and the field is disabled.
Is there any reason why users cannot change their username? Or are there any plans implementing this change?
If it's by design, can at least the greeting text in e-mails be referring to the nickname, instead of numeric username?