After reading Facebook’s blog on Messages, I thought I should write down some thoughts:
“Messages is not email. There are no subject lines, no cc, no bcc, and you can send a message by hitting the Enter key. We modeled it more closely to chat and reduced the number of things you need to do to send a message. We wanted to make this more like a conversation.”
As for the Social Inbox, this is an implementation of a concept similar to Gmail’s Priority Inbox. Messages from people I know go into the Inbox, the rest go to the Other Inbox. Pretty simple classification mechanism (and quite effective).
“We are also providing an @facebook.com email address to every person on Facebook who wants one. Now people can share with friends over email, whether they’re on Facebook or not.”