Last week Facebook sent out a cryptic invitation for the press to “come see” what they’re up to, leaving the entire Internet to speculate about what exactly Facebook is up to.  Theories abound, but today we will learn what Facebook is hiding up its sleeve.

At 10:00am PT in Menlo Park, California Facebook will unveil …something.  There is a lot of speculation about what that might be and what Facebook has planned for today.

One popular theory is that the folks at Facebook will be launching a mobile device. Facebook CEO Mark Zuckerberg has denied that any type of mobile device is being developed, but as Search Engine Journal suggests, doth he protest too much?

A mobile device would make good business sense, but it isn’t exactly in Facebook’s wheelhouse.  Those who have seen The Social Network know that the people over at Facebook are code junkies, and physical technology is just not what they do.  That’s not to say that Zuckerberg can’t expand, but it would be an unnatural transition for the social giant.

If a Facebook phone is the big secret that Mr. Zuckerberg has been hiding, it bodes well for Facebook investors who have been less than thrilled about Facebook’s stock performance after their IPO last year.  A mobile device would generate much-needed cash flow into the company and, as we’ve discussed before, monetizing always is always struggle for social networks — even powerhouses like Facebook.  Popularity does not necessarily equal income.

Whatever the news is, we’ll be sure to keep you posted on Facebook’s big announcement.

UPDATE 1:11pm ET: Mark Zuckerberg took the stage moments ago, announced that Facebook will be upgrading it’s internal search capabilities. For example: rather than having limited filters on only public content, users will now be able to use search queries such as “My friends who like Star Wars and Harry Potter” or “People named ‘Chris’ who are friends with X”.

How do you feel about the announcement? Will this new Google-esque feature come in handy?