Is there any particular rationale for this? I mean I log into iCloud, google, yahoo, my bank, facebook, etc with my email. It's a required unique identifier that is used to create an account here. It makes absolutely no sense that you would require people to login with a second abstract string that they're prone to forget such as what I just did.
Had I not made this thread, I'd be trying to figure out how to track down what my username was.