Facebook has announced that the address people type into a browser's URL bar to reach a user's timeline will now also be used to send that same user email. For example, if a user has an email address for Facebook that is facebook.com/johndoe11, that same user can be sent email on Facebook using the address email@example.com
Facebook made the announcement yesterday, stating that the feature would begin rolling out immediately but will take a few weeks to reach all users. Don't worry, though, if you have already chosen a different email address for Facebook email: Facebook will let leave it untouched, allowing you to keep your chosen address.
Facebook unveiled its @facebook email functionality in 2010. It was a bid to consolidate email with other communication avenues such as instant messaging and text messages. Facebook rolled out its vanity URL service in 2009 to encourage easier sharing of individual Facebook pages. Making usernames standard for both features is a no-brainer and ,frankly, I'm surprised it has taken this long for the two features to be combined in this way.
If you still don't have a Facebook email address or vanity URL you can still sign up for your Facebook username here.