How is this supposed to work?
When I click "Log in using OpenID" the user/pass form disappears, "Log in" button and link "Cancel log-in via OpenID" are displayed.
When I click the button a message appears that I need to enter password, which is obviously wrong. (This happens even when I entered my OpenID in the username field.)
Tested in Chrome and FF.
Either it does not work at all, or it is just a very poor UI-design.
--
Your OpenID: [_____________________] [Submit]
--
How hard is that? 
I'm sorry if it sounds harsh, but I've been forced to create YET ANOTHER ACCOUNT because the UI does not work. 
I have OpenID identity couple of years now and I was able to ue it only on Stackoverflow.
Regards
J. Záruba
P.S.: No, I was not forced, I just wanted to say thank you to one poster for pointing out a solution for issue that is not mentioned in the documentation.