I also think that improving the error message described in http://reddragdiva.dreamwidth.org/30773.html?thread=70965#cmt70965 to give an LJ example including underscores would be a help. I think there's another bug already open to make it guess sensibly for people with underscores in their usernames, which will also help

This is all that is required IMO. A simple example or examples of how to log in using OpenID will satisfy 90% of those people attempting to use it.