Lots of sites nowadays offer the option to log in via Google, Facebook, LinkedIn and so on, and sometimes a standard username/password option as well.
While this goes a long way toward helping users avoid managing credentials per site, it poses a new problem: now users have to remember which openid provider they used when they registered with the site. I can attest to this myself; there are plenty of sites where I can hardly remember if I registered with Twitter, Google or what..
So the question is: should sites offer multiple openid options (to increase the chance of registration) or stick with just one (e.g. google) to not confuse returning users?
Remember that unlike with normal user/pwd registrations, password managers like LastPass can't really auto-fill a social-sign-in form for you. So offering regular basic authentication plus one social option is ok, since password managers/browsers will let you know if you have registered with a password or not.