So Facebook’s “Gmail killer” is not. CEO Mark Zuckerberg said so. I agree; it feels more like advanced IM than next-gen email. The new Facebook messaging system offers a single inbox that potentially unifies email, Facebook messages, IM, and SMS – all your one to one communications (but no voice). It offers a priority inbox by routing your friends’ communications higher, and a user can adjust that. That makes for an automatic “white list.” It maintains all messages between you and any given friend as a single thread. It’s optimized for simplicity and immediacy – for instance, it’s a little hard to tell from the demo, but I think if you respond to any message the default reply mechanism is IM if the user is online, rather than the original “medium.” Most people treat IM as ephemeral conversations, rather than log them, but as with Groups, this is more about changing behavior going forward than about filtering history. Zuckerberg said 350 million Facebook users use its current messaging, and 1:1 message (IM, messages) traffic is growing faster than its user base. Live blog of the event and Q&A is here.