Unknown to most, Facebook actually offers @facebook.com as your email address. Currently, it is invitation only but you could request for invitation here
The chatters have speculated that this is a way for Facebook to compete for user base with the other email services offered by Google, Microsoft and Yahoo! but this if this is true then they need to really finish it up and get it out of Beta stage. Gmail will always gets new users with new Youtube and Android users while Windows live is still the most widely used email service around the world, in the same time, Facebook have a very very big user base.