Paypal allows you to send money to someone by entering their e-mail address. Is this the best practice for money transfer services? Would it be more user friendly to use user-picked usernames instead, ...
When the username for a service is an email address should the field be called 'username' or 'email'?
What is the best solution for an app : Email or username field? I like email because: it's unique user will easily remember it's personal (which can be a disadvantage sometimes; Multiple users on ...