What are the pros and cons of using an email address as a user id?

Question

I\'m creating a web app that requires registration/authentication, and I\'m considering using an email address as the sole user id. Here are what I see as the pros and cons (upd

Answer 1

CON: If I change my email address, suddenly all my account names are invalid. My name doesn't change, but my email often does. I have occasionally revisited a site after a number of years, and been stuck... what was my email address two years ago???