Gervase Markham’s writes about the changes to your Facebook profile, where now by default a @facebook address is shown instead of your own email address:
The email instead goes to my Facebook inbox, and I don’t get a notification email to say it’s there.
So this is why Facebook introduced it: They want you to go to their site to check for email. They don’t want to send the messages to your email and have you interact there, they don’t want you to use a search engine to find content, and they don’t want you to use forums and instant messages to talk to people. They don’t want you ever to get the idea to leave the site.