Have you done any testing to see how many users you lose by doing this? There is, after all, a percentage of your users who will see your "login with Yahoo" me

Have you done any testing to see how many users you lose by doing this? There is, after all, a percentage of your users who will see your "login with Yahoo" message and not understand what you mean, then leave when they can't find a way to register. You seem to think that number would be low. Experience with users & registration leads me to believe that it will be quite high. I personally don't plan to implement openID, so I can't do any testing. I'd be curious to see what your numbers say.