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.

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.

Google (GOOG) just picked up another promising startup in its effort to gain some ground in the online visual advertising market. Teracent, which was formed three years ago, is becoming part of the search engine giant.

Yahoo! (YHOO) currently leads the market in display advertising sales, and Google has been trying push into the space. Last year, this led to its acquisition of online ad service DoubleClick, but that was a first step rather than a total solution to Google's display ad ambitions.

Bebo is the largest social network you never heard of, and Yahoo! (NASDAQ: YHOO) has locked up exclusive rights to sell display ads on the site's UK and Ireland sections. That will add 11 million unique users to the Yahoo! ad network. Bebo said its is interested in Yahoo! handling its business worldwide. That would bring Yahoo! a total of 38 million users to add to its display arsenal.

Yahoo! management told Reuters: "It's a core step for us in building up the largest and most effective advertising network. It's a big deal." Bebo says it picked Yahoo! because of its ability to target display ads based on things like user behavior.

While the deal is clearly good for Yahoo!, it merely pushes it further into the slowing market for display ads. Industry experts expect internet advertising to rise 25% in the current quarter, with the fastest growing part being text ads in search results. Display is expected to lag well behind.

For Yahoo!, Bebo is a good deal in the weak end of the online market.

Douglas A. McIntyre is a partner at 24/7 Wall St.