We've had a rash of new users trying to register using their email addresses as usernames.
For the privacy and security of all of our members, this is not allowed. Email addresses, phone numbers and other features that could permit a spammer to harvest and stalk our members are all expressly forbidden.
If I spot a new member with an email address as a username I will change your username. You will not get a warning beforehand. I will just change it. The system requires me to also change your password when I change your username. It automatically generates an email to you with the new login credentials.
Therefore, if you are one of the many people who have recently registered using your email address as your public username and can no longer access your account, make sure to check your email to find out your new login information.