It should be noted that MailChimp is huge. I have no figures, but I'm guessing they have millions of users. This means that problems that affect 0.1% of their u

It should be noted that MailChimp is huge. I have no figures, but I'm guessing they have millions of users. This means that problems that affect 0.1% of their userbase still represent a nominally large number of users. They don't have problems like user acquisition and brand recognition. For me, adding 'signup with Facebook' has increased the number of registrations. I'll worry about the effect on failed logins when it proves to be a problem.