Facebook Mobile has been rapidly expanding its reach, growing from 100 million users per month in February 2010 to 250 million users per month in March 2011. Should this type of growth continue, there could be upside to our intrinsic value estimate for Facebook, which we currently peg at $45.1 billion. Facebook competes with Google, Yahoo, Microsoft, AOL in the text and display advertising market as well as the search advertising market.

Facebook primarily competes with Google (GOOG), Yahoo! (YHOO), Microsoft (MSFT) and Aol (AOL) in the display and search advertising markets. Here we highlight three major revenue streams that contribute to Facebook's value.

We currently peg Facebook's intrinsic value at $45.1 billion.

Facebook primarily makes money through online advertising, both display and search advertising, in which it competes with Google (GOOG), Yahoo! (YHOO), Microsoft (MSFT) and Aol (AOL). However, it has started to tap other business lines as well, like distribution of virtual goods in games and applications.

Time Warner Offering Movies on Facebook Fan Page

Time Warner (TWX) recently announced that it will start offering movies for purchase or rental through Warner Brothers Entertainment's Facebook fan page, making it the first studio to do so. The users will make the purchase with Facebook Credits, a virtual currency. This is no doubt a good move by Time Warner as it gives the company a platform to tap the increasing base of users looking to consume traditional media entertainment online.

The sale of DVDs is going the way of the PC -- both have seen their market share dwindling. In a world of instant information, streaming videos are replacing DVDs. Last year, DVD sales fell by 43% to $7.8 billion from $13.7 billion in 2006, The Wall Street Journal reported.

There is another accompanying trend that reinforces streaming videos. Customers are spending more time online. Add the multiplier of time spent on social networks and it's streaming video hands down.

Google (GOOG), which competes with Microsoft (MSFT), Yahoo! (YHOO), Aol (AOL) and Facebook in the search advertising market, has been working to increase its penetration in social networking. It started with Google's foray into social applications like Google Wave and Buzz, which did not meet initial expectations. Google then made a number of acquisitions for the development of its major upcoming social networking project named Google Me.

The U.S. online display advertising market saw a revival in 2010, with an estimated growth of 17% over 2009. Continued growth means greater competition amongst players like Yahoo! (YHOO), Facebook, Google (GOOG), Aol (AOL) and New York Times (NYT).

We currently maintain a $17.88 price estimate for Yahoo, in line with market price. Display advertising accounts for roughly 18% of Yahoo's stock value by our estimates.

Since 2006, the number of registered users on Facebook has seen near 100% annual growth. We estimate that the number of registered users has increased from around 10.5 million in 2006 to around 595 million in 2010 and has since continued its upward climb. From the time Facebook decided to allow any user above the age of 13 to create an account, the website's number of registered users has seen a meteoric rise.

"Microsoft (MSFT) recently released its fiscal second-quarter results; we felt results were really quite strong, with solid gains in most segments and good cost discipline," says Geoffrey Seiler.

The editor of Bullmarket.com explains, "If these results were from another company, the stock likely would have gotten a lift. But Microsoft is the Rodney Dangerfield of companies: it doesn't get the respect it deserves.

"Microsoft reported net income of $6.63 billion, or 77 cents per share, compared with $6.66 billion, or 74 cents per share, in the year-ago period. Sales grew by 5% to $19.95 billion from $19.00 billion.

There have been rumors for some time, fueled by occasional comments from News Corp., that the media giant's days of owning also-ran social network MySpace are numbered. News Corp. COO Chase Carey indicated that MySpace may be sold or spun out when he spoke on the company's earnings call on Feb. 2.

Buried in a line item of the News Corp. (NWS) fiscal second-quarter earnings release were the results of MySpace, under the category of "Other." The description of the segment was: "The Other segment reported a second-quarter operating loss of $156 million, which is $31 million greater than the prior year. This decline was primarily due to increased losses at the Digital Media Group, stemming largely from lower search and advertising revenues at MySpace."

One of these days, Facebook is likely to go public. But how much could its shares be worth in an initial public offering? The numbers are all over the place. From Bloomberg's estimate late last year that it was worth $25 billion to Fortune's estimate last August of $50 billion. Now, there is another report from a financial research firm, Trefis, that pegs the value at $45 billion today -- but potentially as much as $125 billion, if a few things go right.

One of the things that could go right, is coming up a with a new way to generate revenue -- and Facebook says it has a plan. It's called "sponsored stories." The company plans to pull content out of members' status updates for use in advertisements that will appear in their friends' Facebook pages.

After a successful stint at PayPal, Reid Hoffman started LinkedIn in 2002. He did it from his living room.

Now LinkedIn is the largest social networking site for business. And yes, the company has filed to go public. The lead managers on the deal include Morgan Stanley (MS), Bank of America (BAC) and JPMorgan Chase & Co. (JPM).

Yahoo is still trying to play catch up. Helped by cost cuts, Yahoo! (YHOO) posted late Tuesday fourth quarter income of $312 million, or 24 cents a share, more than double last year's income of $153 million, or 11 cents a share, according to the Wall Street Journal. Revenue fell 12% to $1.53 billion from $1.73 billion.

Net revenue, which excludes commissions paid to partners, fell 4% in the quarter to $1.22 billion from $1.26 billion in the year ago period. Excluding the Microsoft (MSFT) impact and certain divestitures, revenue grew by 2% in the quarter.

A key to the success of Goldman Sachs (GS) has been its ability to anticipate major trends. For example, it did this during the 1980s by providing protection against hostile takeovers. Of course, then there was the move to proprietary trading.

However, in light of the Obama regulations, Goldman has had to make another major shift. In fact, it looks like the firm is going back to its roots of providing top-notch advice on public offerings and M&A.