I actually do not login to website that asks me login either using Google a/c, Facebook or so. Twitter being an exception because everything at Twitter I've anyway made public, but I hesitate still.
That's a strange opinion to have though, because before doing login through either of these services, you will be asked if you want to give that app permission to certain parts of your account. For example, I might have you log in through Google to verify your email and I don't see a reason why you wouldn't let me see it; you've already shared your email with my app to register an account in the first place.
Most of the website, do not just ask Email. Most ask other info too, like my DOB, full name, Other Profile information. And when I say I "do not use", I am talking about the first time logins of course. I don't really know what kind of a website it is, legit or just a vapour. And I do not know in advance what information it will ask.
Take the example of The Old Reader, till recently they wanted to take control of your Contacts too(along with Reader; now they don't). I knew it once I was at past the Google SigIn page(and I aborted right there). It was frustrating even for those few seconds. Many do this.
So, I have given up on them altogether.
I mean I have OpenID accounts set up especially for this with the data I would like to provide for this. There Mozilla's Persona(it's Identity Management System)- etc. Why not use these?
And do not even get me started on Facebook. I don't open a website again if the only way to login was via Facebook. Paranoid? No, rather pissed off. (By the way, whenever I tried using Facebook logins the above mentioned problems surfaced only in bigger multitude).
Because everyone has Google, and the lowest setting on Sign in with Google+ contains some personal information from your account, including things like DoB, Full name, etc. Google recommends OAuth2 over OpenID for authentication, and I'd rather be using the service Google supports the most in order to provide the best experience to users.
Just because you use OpenID and Persona doesn't mean that the majority of people will. But the majority of people will have a Gmail account, or a Facebook account.
