For geeks it is no big deal to use an URL when they have to login somewhere. But for non-geeks it is probably a bit strange if they have to identify themselves with an URL.
To make it easier for those users to use an OpenID, JanRain — the company behind the OpenID libraries for different platforms — created a widget called ID Selector, where the users have to choose their OpenID provider and enter the user name part of their OpenID. So they do not have to remember the complete URL. Here a screenshot of how it looks like:
You can see it in action on https://www.idselector.com/user/login.
A “disadvantage” of ID Selector is that there will be ads (even though I haven’t seen any while testing), something you may not want…