You get more signups, but people tend to forget which social platform they used for logging in. The more social login buttons you have, the more duplicate accounts people will create by accident.

So in order to REALLY track unique users, you now have to account for duplicate signups, which is not trivial at all.

I think social logins offer a better user experience than email signups, but unfortunately we pay a price for this. Mailchimp blogged about this issue, they actually went back to email-based logins.

(Twitter & Facebook may very well be the right choice for ProductHunt, but be careful with the signup data, is all I’m saying ;)