Want to know why I really don't care for single sign-on? Let's pretend I want to sign into StackOverflow.com.

The Flow

Oooh! I want to check my reputation on StackOverflow! Oh crap, this is a new computer. Let me log in!

Huh. Well, let's check 1Password.

Shit. I didn't save my password. Oh wait, maybe it was Google?

Okay I think it's the second one.

Um. Okay? Allow.

That wasn't it. Let me click Back and see if it was Facebook.

I guess I'd like to continue as Aaron since that's me?

Yay!

The Reality

I originally signed up with my first Google account listed. I did NOT sign up with Facebook. After logging in with Facebook it automatically matched my account based upon e-mail address and let me in. StackOverflow is assuming that e-mail address changes on the trusted third party system are verified. I can imagine at least one of the "more login options" services would let me change the e-mail address to another user and ghost in as them using this.

In any case StackOverflow handles account creation decently. I've tried this SSO login on other services I didn't have in 1Password with more stabbyness. Sometimes a new account is created every single time I choose a different SSO account.

I know I'm in the minority of most users having multiple Google accounts but I do know plenty of Facebook users with more than one. I'd rather have a known set of credentials than play the guessing game of which account was it.