How important is social sign-up to attracting new users?

Question

Many website, including this one, are using social sign-up to speed up new user registrations. I'd like to know what are the adoption rates of this service, and whether there are any pitfalls to using social sign-up, e.g. users wary of their Facebook accounts being raided by the host site?

Background: What I'm calling 'social sign-up' (probably goes by many names) allows new visitors to a website to create a new account via the credentials of their Facebook, Google or other account provider. Many sites implement this with Facebook only, e.g. SoundCloud, while other site offer the full range of account providers, e.g. SE. Gigya is a company offering CMS plug-ins to create this functionality easily on a site. Social sign-up is slowly becoming ubiquitous, but I'd like know if it's a net benefit or if there are pitfalls to this. One could argue that any additional registrations a site gets via this method makes it worthwhile. But it could turn out that social sign-up users tend to be non-commital users that make little contribution to a site's community and goals. My questions is asking for hard data and personal experience about this relatively new approach to authentication.

(Maybe I should post this in Meta to ask for SE's own stats on this.)

Answer 1

It's good because it significantly decreases the user effort. For example, most people probably already have a Facebook, Google, etc account. Re-using it makes it way cheaper for people to register. Typically, registration is a surprisingly thick barrier. When The Times tried to get people to register to read the news, even without paying, their readership dropped very dramatically.

When the user sees the "register" button, they read "hassle". When they register with Facebook, Google or whatever, then it removes that punishing time waste of filling out your details for the billionth time.