Two years ago I removed Google logins, since Google's OpenID support was being shut down. Today, logins via Google are enabled once again, but this time via Google's OAuth. The practical upshot of this: your identifier is your email address.
This is a good time to mention that Mozilla has announced shut down of their Persona/BrowserID authentication platform. If you've been using this, it's a good idea to start using Google login instead. Either that, or add in an alternative OpenID identifier to your account (available via the profile page).