From my experience with a B2C site, we see around 50% use password and 50% use social logins.
The problem however is that people easily forget what they used to login with, and when they try things like a password reset, we can't really reset their passwords if they used social logins. Or they might forget whether they used google or facebook to login...
So the main problem that I personally have with social logins is that they create fragmentation, and a simple login form becomes a memory-exercise for the user.
That's why I avoid using social login buttons. I have a password manager, so remembering passwords is not a problem. However, remembering if I logged to this site with Facebook, Twitter, Google or something else is.
If users sign up through a social site, their account is still identified by email. So as long as their email addresses are the same between sites, it doesn't matter which social service they use, so they won't have to remember. Twitter doesn't provide an email address, however, so that could be a problem.
yes, you're right about twitter. However, we don't have that much of a problem with people hitting the social login button as much as with people forgetting that they used social last time they logged in.
They then try to enter email and password. When it rejects them, they try to reset the password, and get frustrated that the reset password does not work...
We relatively regularly answer support emails and just tell users "It looks like you used your google account to sign in last time, just hit the right button and you'll get in instantly"
Not only that, Facebook's default privacy settings are set up in a way which most users' proper email address is not exposed to sites using social login.
Google logins are the absolute worst, now you have to remember which of your accounts you logged in with (like many others here I have 5 active accounts - I really wish they could give me a single identity that would work with all of them).
I have separate google identities because I have a gmail account and my work uses Google Apps; I also have another account that I use for YouTube which I refuse to merge into my gmail account (if that's even possible).
I don't want to merge them together because they're separate accounts for separate purposes, but that's a difficult position to keep because of how absurdly difficult it can be to deal with multiple google accounts. Even though Google supports multiple accounts, their base assumption is that people have exactly one Google account which is exactly one identity which incorporates all of one person.
I've been unable to accept calendar invites sent to my work account because Google Calendar insisted on opening to my personal account when I clicked the link; even if I opened my work calendar using the drop-down, and closed the other window, the link would only open to my personal calendar and then tell me 'you don't have access to this calendar'.
It feels as though the parent poster was asking for Google to understand that one person can have multiple accounts, rather than assuming a 1:1 mapping between the two and behaving as such.
I have one gmail account and 4 different google apps accounts (one so I can have a personalised email that I've had for 15 years, the other 3 are different companies that I'm involved with). I use trello with 3 of those accounts but i only want one login, hence the confusion...
Frankly I would like to have only one login with Gmail which requires triple authentication (password + image or something else + phone or dongle or heartbeat or something), then for everything else just email me a link to log in.
The problem however is that people easily forget what they used to login with, and when they try things like a password reset, we can't really reset their passwords if they used social logins. Or they might forget whether they used google or facebook to login...
So the main problem that I personally have with social logins is that they create fragmentation, and a simple login form becomes a memory-exercise for the user.