well there are two different issues that overlap a good deal. 1. wanting a way to uniquely identify a user that is easy for the user to remember (email works g

well there are two different issues that overlap a good deal. 1. wanting a way to uniquely identify a user that is easy for the user to remember (email works great) 2. wanting a way to prevent users from creating duplicate accounts Using emails works great for 1 and is a decent low bar for 2. There are no good answers for 2 so using an email address is the best I have seen.