OpenID is a very useful thing, unfortunately it's hard to remember the provider URL somtimes. Google in particular has a very long URL.
It would be helpful if the OpenID plugin comes with a preconfigured but editable (plugin settings) list of providers like yahoo, gmail, etc. For the login process, the user should have a combobox to select from those providers or to select "other" and enter the URL.
When "other" was selected, the plugin should save the URL and propose to the administrator to add the provider to the provider list.
This would help to reduce confusion for 1st time OpenID users.