Facebook 去掉了用户名，因为用户名是通过 Facebook 发送电子邮件的一种方式.

Facebook got rid of the username because the username is one way of sending emails via Facebook.

例如，给定 url http://www.facebook.com/sebastian.trug

相应的 Facebook 电子邮件将是 sebastian.trug@facebook.com

the corresponding Facebook email would be sebastian.trug@facebook.com

如果通过电子邮件发送，将直接接收到 messages(如果 message 设置设置为 public)，否则接收 messages代码>其他代码>收件箱.

which, if emailed, would be received to messages directly (if the message setting is set to public), otherwise to the other inbox.