Detractors of Facebook's $15 billion valuation make a strong case, as well. Analysts argue that Facebook's value has probably declined as badly as, if not worse than, that of Google or Yahoo! (YHOO Quote).

In October 2007, Microsoft had invested $240 million in Facebook for a 1.6% stake, bringing the overall value to $15 billion. In the deal, Microsoft not only bought preferred shares to make sure it would get paid first in the event the Facebook was acquired, but it also secured an advertising deal and elbowed Google out of the picture.

Since then, Google shares have plunged more than 40% to $323 a share, while Yahoo!'s stock has fallen more than 50% to $13. Even Microsoft has dropped 31% to $20. It's not hard to believe that Facebook's value has slid dramatically, as well.

As the economy has deteriorated, Facebook -- like many companies -- has been in need of more cash. In a December article, Web site TechCrunch reported that Zuckerberg confirmed that Facebook's $15 billion valuation round was still open and that the company's CFO Gideon Yu was open to new investors at that price.

Zuckerberg denied, however, that Facebook was searching for new investments at a lower valuation. "We're not actively going around trying to raise money from a lot of different people. It's more just a follow on to that [previous round]," he told TechCrunch.

No matter what Facebook is actually valued at, some analysts wonder if the company's ability to transform itself into a major tech player even exists, and that could be a major concern for Microsoft investors. Jeffrey Lindsay, analyst with Sanford Bernstein, argues that Facebook was the last best shot at an Internet initial public offering in the U.S.

"Facebook missed a golden opportunity for an IPO, which they may not have realized was there and won't come again for many years," Lindsay said. "In theory, the deal with Microsoft was a technical valuation, but that should've been the moment they seized the day. They had the chance but blew it. It would take something pretty spectacular to bring them back now."

With the likelihood that users will migrate way from Facebook, the same way support for MySpace faded, Lindsay says that Facebook blew their chance for massive growth. Lindsay says that as more users enter Facebook's gated community, the more likely it is that people will move on to the newest Web 2.0 product.

"There's a very strange dynamic with social networking properties where they get so large they lose their exclusivity. People start to drop out of them," Lindsay said. "Facebook is at a point that MySpace reached some time ago. Facebook is so 2007 now, and MySpace is so 2006. People are finding more exclusive ways to group together socially."

Lindsay is also quick to dismiss the importance of Apple's decision to tie its iPhoto software to Facebook. While hardware manufacturers and photography software players have discovered face recognition technology as a feature attribute, one that will help to sell cameras and photo editing software, he argues that to make a direct benefit to Facebook is overstating it.

"The new photography innovations are very helpful to the social networking players. They're definitely beneficial, but they're not transformative," he said. "It will not give them a new lease on life."