[RandallBrown]

Using an email address instead of a username is SO HUGE of a usability win. I can't stand when companies don't do this.

My email address is going to be unique. I don't have to pick one of the few standard usernames I use and hope that it's available. I know my email address will be.

Have you ever been to a site that says username, but really wants an email address? It's absolutely infuriating.

[bwooce]

I struggle with this. I acknowledge all your points, but it doesn't cover the usecases of: 1. Changing ISP and getting a new email address. This is really common. 2. Having multiple addresses (work/home, etc). Also see #1

This breaks password resets and creates a "I want to change my credentials" flow that doesn't exist with usernames. It is especially complicated as emails to the old address won't work/are not accessible.

Most companies want to keep track customers over their lifetime and not have them create a new account when they change ISP/job.

If you want to see an example of this not working at all well, see Apple IDs. The pain surrounding them, purchases, @me.com, @mac.com, changing countries and the attached purchases is inspirational in its depth and breadth.

[JeffL]

We used to require an email for signing up for our game, but when trying to actually email people, nearly half the emails provided turned out to be fake or bounce for some reason. My takeaway from that is that people don't want to give out their email, so we stopped requiring it. Does anyone have any measurements on if requiring an email instead of a username reduces the number of sign ups?

[chris_mahan]

I use several email addresses for login, including some that are no longer active. When I forget my password on those, I just orphan the account.