Going by email? I like it. I used Google to sign up for the Ubuntu Discourse, I made a regular account here, and I think I used Twitter somewhere else. This would mean that authentication provider miscreants like me would just have our settings no matter what, provided that whatever service we used was tied to a common email, correct?
If someone is so morbidly curious about how I read things on the Internet that they wanted to find my email, MD5 it, then go look at my settings … I say my God that’s creepy but I don’t really care.
I doubt that my settings from site to site would vary much, but I could imagine wanting to be able to override certain things on certain sites. I’m sure that would be provided for, as well as some means of opting out of the whole thing.