OpenID Usage Statistics from

Check this out. Web service had 12.2% of their new users register on their site using an OpenID in the month and a half between mid December and the end of January. And their OpenID users were significantly more active users when compared 'normal' registrants. OpenID adoption among websites and services is still very minimal, but this study is a start of what I think will be a very strong case for implementing OpenID in the pretty near future.