Personally I interact only on web sites where I can register with my email address. The sites you listed are those that I avoid more, I don't like knowing my co

Personally I interact only on web sites where I can register with my email address. The sites you listed are those that I avoid more, I don't like knowing my comments are tight to my personal identity on a service that does also manage content. ie. I would be ok using an OpenID from a company that does only OpenId. FB/Google/etc. authentication platform is just a way to build up their userbase to make money out of user profiles (which is not necessarily bad, but I don't want to be a product just because I need to post in a forum).