If you’re a social gamer, i.e. one who regularly plays free-to-play games in short doses, most probably on Facebook, chances are you’ve come across a Zynga game or two (or 6 out of the top 7 games). And while we know that Zynga certainly has a valuation on not only their properties, but the company itself, I’m not quite sure anyone would have guessed that this valuation would be in the $5 Billion range. This figure is according to an investment report issued by investment news blog Second Shares yesterday.

While Zynga has no short term plans to go public (at least that we know about), industry analysts Jay Gould, Lou Kerner, and Bill Auslander estimate that if Zynga were to go public tomorrow, shares would trade around the $15.75 per share mark. This estimate is determined based on a multitude of factors, one of which being the price that current Zynga employees could fetch on the secondary market by selling their stock options.

Keep in mind – these estimates are conceived through complex financial projects and mathematical computations. I’m not going to use the word, but it should have already occurred to you where you might have heard this terminology before (can you say derivatives?).

However, financial wizardry aside, the Second Shares report highlights that Zynga is clearly leading the social gaming industry. Their MAU (Monthly Active Users) clocks in a massive 237 million, with the nearest competitor, EA via their purchase of Playfish, hits the finish line with a respectable 53 million, but still dwarfed by Zynga. The only other player mentioned that is significantly larger than Zynga is Chinese firm Tencent Holdings with an MAU of 400 million. As a reminder…Tencent is testing the Facebook waters.

Naturally, with a number this big, there’s bound to be a few folks scratching their heads, and asking…Why? How? Etc…Notably, LOLapps CEO Kavin Stewart has suggested that Zynga artificially inflates it’s MAU numbers by counting the same user over multiple applications. For instance, the Second Shares report specifically points out that Zynga receives 15 MAU from the FarmVille.com, indicating that the MAU may not be a proper valuation based on a single platform.

Building on this theme, while the report considers Zynga a strong investment opportunity, it does highlight some of the risks involved. Currently, Second Shares says that 50 percent of Zynga’s revenues are generated from one title: FarmVille. As well, 35 percent of Zynga’s MAU is generated from FarmVille alone. And adding to this house of cards, Second Shares also points out that users use FarmVille 50 percent more than any other title.

As a veteran of the first dot-com boom, I can only think of one very valuable token of advice bestowed upon us from the venerable and wise writers of Battlestar Galactica, “All of this has happened before, and all of this will happen again.”