Many investors are seriously wondering about the inherent value of investing in Facebook during the upcoming IPO. According to data compiled by our friends over at Bloomberg, the proposed valuation of the social networking giant puts it above almost all the members of the current S&P 500 index. In fact, the only companies it didn’t beat Amazon.com Inc., Leucadia National Corp., and Equity Residential.

As we reported yesterday, Facebook is offering 337.4 million shares for $28 to $35 per share in their upcoming IPO. If the stock really takes off, co-founder and CEO Mark Zuckerberg’s share of the company would be worth $17.6 billion. According to Bloomberg, this would make him richer than Microsoft’s Steve Ballmer, and Russian Steel billionaire, Vladimir Lisin. That would be pretty impressive considering he’s about half the age of both men.

But, as you know, the ultimate price it sells for could be higher or lower depending on the demand. Facebook isn’t just popular because it will give good returns to shareholder (if that indeed happens), but because so many people use the service everyday, 900 million to be more exact.

Despite this buzz around the IPO many investors are questioning the value of investing in the California-based company. Francis Gaskins president of IPOdesktop.com believes that that Facebook has already seen its high-growth days and that it might be a bad investment.

Gaskin comments on Facebook:

“Obviously slowing down”

“The company is entering a maturation process,”

We will have to wait and see what demand is like once stock goes on sale. It will be interesting to see what investors are thinking by the time May 18th rolls around. We’ll keep you updated on all the happenings from the Facebook IPO roadshow and the May 18th IPO.