Best openid implementation

I think OpenId has a lot of things for this. But the biggest beef I have with him is convenience. Especially technically ill-conceived people understand that they need to choose a "provider" to log into the system. Stackoverflow's login implementation is pretty good, but I think it will cost me a pretty detailed explanation to get my mother to use a gmail account here to register / login to another site ...

So the question is, does anyone know about OpenId registration / login capabilities that are more useful than Stackoverflows?