Sorry I was not clear and it is not terribly important. I've just wondered what it actually means to be "registered." If I have recovered my cookie-based account it means the account has been verified by e-mail. I'm just wondering isn't that a form of registration without having to have used OpenID?

Its mostly a distinction between "can login with one click (Registered with OpenId/Facebook)" and "can login with a crazy convoluted path (provide email [again], check email for link, etc.) (Unregistered)".

You can get the lion's share of a Stack Exchange's utility without registering, and this is quite intentional.

I just tried a test post and it won't let me proceed without putting an email address in.

Ah, my bad; been a long time since I've had to do anything as an unregistered user, mis-remembered.

Looking at the code, we do require something that looks like an e-mail, for recovery purposes (I assume, that code predates me by a bit). It is not, however, verified.

It appears to do a basic regex to validate the e-mail address but does not require a confirmation e-mail to be sent to post comments.