I have implemented [janrain's social login](http://www.janrain.com/products/engage/social-login) on my website. I am wondering how important it is to include a traditional login (email/password) system.

I believe there may be a significant percentage of potential users that are either uncomfortable or unfamiliar with social login. These users may not sign up for my site if social login is the only option.

Does anyone know of any data comparing social login vs traditional login and the corresponding adoption rate?

Is there a current best practice? Do I need to give the user an option to sign up using username/password? Or is facebook/google/openID/twitter/MS/Yahoo enough?