In short, Facebook will have to open up the books

Facebook is reportedly acknowledging that it will surpass 500 individual shareholders this year--which would require the company to open up its financial information by April 2012.

There are a lot of rumors and speculation afoot about Facebook's $500 million funding round led by Goldman Sachs and the investment bank's subsequent private offering of Facebook stock to deep-pocketed clients--more speculation, in fact, than there usually is around news pertaining to Facebook.

But one thing stands out as fact: should Facebook hit the threshold of 500 individual shareholders, it will be required to either start trading publicly or at least begin disclosing its financial information, according to rules set by the U.S. Securities and Exchange Commission. At the end of the fiscal year in which it reaches this milestone, it has 120 days to comply.

A number of news outlets claim to have seen a set of documents distributed by Facebook to prospective members of the elite Goldman investor bunch, and the documents assert that Facebook will surpass that 500-shareholder margin in this fiscal year, which jibes with the calendar year for Facebook. Basically, the company is acknowledging that about 120 days into next year--by April 2012--it'll be forced to open up the books.

What's less clear is whether it would disclose its financials while remaining privately held, or actually go public. A Facebook IPO has been talked about for years, but investors and executives at the company have repeatedly fanned away rumors and have said there would be nothing until 2012 at the very earliest.

Facebook founder and CEO Mark Zuckerberg has been notably hesitant to go public. Much of this has been about preserving the culture of Facebook's early days, and Zuckerberg's belief that the feel of a start-up is preferable to that of a huge company--$50 billion valuation be damned.

Facebook has managed to keep its shareholder numbers low because of a 2008 change to its stock structure in which new employees were given stock that would not vest until the company went public--which does not require that stock to count toward the tally approaching 500. But early employees and investors have been trading Facebook stock so actively on private markets, even before the massive Goldman Sachs deal, that it had already piqued the interest of the SEC.