We’re all using tons of apps these days on our mobile devices and desktops, many of which are using these social login buttons. Sometimes you log in with Twitter, sometimes with Facebook, sometimes with a username and password specific to that app. It’s hard enough to remember your username and password, let alone which service you should bloody use to log in. As you add login buttons to a page, you also add decision points for users, while creating visual complexity in your design. The marginal gains in login rate are chipped away by the additional cognitive load you’re adding for your users.
If you’re using Twitter and Facebook for signup too you’ve got a bigger problem. A user’s credentials are then bound to another account on another service that could be canceled at any time, breaking access to your app without the user knowing.
That’s exactly the reason why I am mainly against social login buttons. It’s a double-edged sword. On the one hand you’ve got a new user without him having much work to do, on the other hand — like Aarron says — you depend deeply on the goodwill of Twitter or Facebook (Remember what happened to Grooveshark).
I think there might be a better way: Let your users connect through one of those services, but add a standard registration form right after they granted access to their Twitter or Facebook accounts. You can pre-fill the form with data you get from those social networks and the user registers an account that is not totally bound to any other network. Win-Win. (via)