In the literal sense that you are not your e-mail, yes email != identity. In a practical "on the internet sense," your email really is your identity (maybe SSN

In the literal sense that you are not your e-mail, yes email != identity. In a practical "on the internet sense," your email really is your identity (maybe SSN or name would be a better description; you can change it, but to do so is catastrophically disruptive). After all if you can't be contacted you really can't be identified, and the universal way of contacting someone online is through email. Now, you should definitely try and provide some redundancy (store multiple email addresses, long living sessions, whatever) and make your anonymous/unauthenticated/drive-by user experience stellar. But when push comes to shove if you can't send them a "forgot your username/password/open-id/samoflange" email, you've lost that user. (anecdote: I've had the same primary email for >7 years)