As expected, is announcing a "modern messaging system" today. Mark Zuckerberg says it's not email. But it might just replace it. Get ready for your @facebook.com address.
Every Ping In One Place
(http://cache.gawkerassets.com/assets/images/4/2010/11/500x_facebookbig2.jpg)
What are the difference between Facebook messages and regular email? It incorporates emails, Facebook messages, SMS, other chat clients. Eventually VoIP may also be in play. Instead of having some chats here and some texts there, every time you talk to someone it'll be come part of a stream of information.
Facebook Messages: Every Email, Text, and Chat In One Place [Facebook] (http://gizmodo.com/5690405/facebook-email)