There’s a strong case to be made that as Facebook and Twitter have amassed such huge user bases we should take advantage of the fact that so many of their users are already logged in and just one click away from entering your app. I know that argument all too well, because I made it to my colleagues. We tried that experiment, and found that while there are some marginal improvements to login failure rate, they come with a price. Do you want to NASCAR-up your login page? Do you want to have your users’ login credentials stored in a third-party service? Do you want your brand closely associated with other brands, over which you have no control? Do you want to add additional confusion about login methods on your app? Is it worth it? Nope, it’s not to us.