What's the real valuation of Facebook? That's a good question and one that's continued to baffle industry watchers over the past few weeks. Since mid-April we've seen reports and speculation noting a possible valuation of anywhere from $2 billion to $8 billion. That's a big spread.

And now word comes via The Wall Street Journal that the Russian tech investment firm, Digital Sky Technologies, wants to invest $200 million in preferred stock at a $10 billion valuation. That's starting to creep closer to the $15 billion valuation that Microsoft paid for the company in 2007 when it invested $240 million for a 1.7 percent stake.

The wild swings in Facebook's worth over the past few weeks indicates just how hard it is to place a value on a money-losing company with a massive audience. After all, the gamble is that Facebook -- with potential revenue this year of $550 million according to TechCrunch -- will one day justify the big price tags now being discussed.

The Journal reports that Digital Sky wants to invest $200 million in the company's preferred stock, and $100 million to $150 million in common stock.

It's almost turning into a game trying to figure out what Facebook is worth. I wonder if the slight rebound in the tech IPO market this week -- OpenTable and SolarWinds both completed successful IPOs -- is having an impact on Facebook's rising fortunes.

Facebook has downplayed the possibility of an IPO, but that would be one way to resolve all of this speculation on how much its worth.

[Update: Facebook confirmed the $200 million investment in an announcement Tuesday]