12:45 PM/ET: We're eagerly awaiting Facebook's mystery announcement. The social network sent out an invitation for the press to "come and see what we're building" and about 120 bloggers and reporters have turned out.
Now we're all in the "King of Ping and Pong" room in building 15, and there's still no indication of what the announcement is about. The signs on the walls say "Move Fast and Break Things," "Fortune Favours the Bold," "Focus," and "What Would You Do if You Weren't Afraid."
(Read More: Facebook Charging $100 to Message Mark Zuckerberg)
Here's what I know: It's not a physical building. It's not a phone hand set. It doesn't involve a big partner-- there's no sign of any other company here. It's some sort of product for users, not something for advertisers.
Read More: Facebook Mystery Announcement: What to Expect
And it surely is all about MOBILE and will have implications for Facebook's bottom line. My bet: some sort of mobile video chat app, a change for Instagram, or some sort of app store/game platform.
(Read More: One Thing We Know Facebook Is Working On.)