My account works pretty well on the other three sites.
But when I log on to Super User, I get:
This is an OpenID we haven't seen before: [openid]
Don't worry about it. Go on and create a new account. Then, in the accounts tab of your profile, associate your SU account with one of your other accounts and you can copy your profile information over.
We improved the message so it now says
But Kyle's answer, above is 100% correct.