Ever since Facebook announced that they were going to providing an @facebook.com email address to every person on Facebook which wants one, I have been waiting for the invitation. I finally got one yesterday and signed up straight away.
After you sign up, you can email anybody directly by going to Facebook Messages and then typing in the email of the person you want to send the email to where you would normally enter your Facebook friend's name. You also have the option of attaching a file or taking a picture or video. However, I am not sure why, when I last tried it, the file attachment function was not working.
However, there are people who are harvesting people's emails by luring them to a fake Facebook email signup app. So be careful.
Watch out Gmail, Facebook mail is here.