I'm a reasonably competent web user.

I've implemented OpenID.

I run my own Open ID server.

I've implemented Shibboleth (and lived!).

I know that Yahoo is an open ID provider, and I think Google is too, but when I'm presented with an old-style (URL) OpenId login I don't have a clue what to enter to use either my Yahoo or Google account to login.

Yes, I know that now most login forms provide easy links to use Google or Yahoo to login. The point is that entering the URL is confusing because no one knows what their OpenID url is, and it isn't standardized in anyway.

The situation is so bad that the OpenID providers had to develop a way for users to enter their email addresses, and then the client performs a discovery request to find their URL.