Carl Icahn, the famous activist investor, resigned from the Yahoo! (NASDAQ: YHOO) board of directors Friday.

This comes just over a year after he scored the position, following the seemingly endless talks the company had with Microsoft (NASDAQ: MSFT) over the possibility of a takeover. Icahn told Yahoo that he was resigning effective immediately because Yahoo! didn't need an activist investor on the board at this time.

Microsoft (NASDAQ: MSFT) isn't planning to acquire its way into the search engine market. The company's CEO, Steve Ballmer, told Reuters that the company would invest in marketing and hopefully complete a partnership with Yahoo! (NASDAQ: YHOO) that is currently involved in a regulatory review. The goal, of course, is to provide at least meaningful competition to search giant and dominant market player Google (NASDAQ: GOOG).

Expect growth to slow a bit for Microsoft, Ballmer says, as a result of global economic developments. In order to cope with this -- and gear up for a potential battle with Google -- the company has frozen its R&D budget of $9.5 billion, the largest in the industry. With that and a $31.4 billion cash and cash equivalent position, Microsoft certainly has the resources to do battle.

Microsoft's (NASDAQ: MSFT) Bing picked up another percentage point of the U.S. search market share in July, bringing the combined Microsoft-Yahoo! hold on the market to 20.36%. StatCounter, which measures and reports internet statistics, puts Bing's search engine market share at 9.41% of the U.S. market, up from 8.23% in June.

The up-tick in Microsoft's performance comes at the expense of Google's. The search engine giant saw its search market share fall from 78.48% to 77.54% in July, according to StatCounter.

The Microsoft Corp. (NASDAQ: MSFT) -- Yahoo Inc. (NASDAQ: YHOO) merger dance is not quite over yet.

In an open letter to his fellow long-suffering Yahoo shareholders, billionaire Carl Icahn disclosed that he has spoken "frequently" with Microsoft CEO Steve Ballmer; "frequently" over the past week about Yahoo. Ballmer indicated to Icahn that the world's largest software company would still be interested in doing a deal ... with one catch.

"Steve made it abundantly clear that, due to his experiences with Yahoo! during the past several months, he cannot negotiate any transaction with the current board," Icahn said. "If a new board were elected, he would be interested in discussing a major transaction with Yahoo!, such as either a transaction to purchase the "Search" function with large financial guarantees or, in the alternative, purchasing the whole company. He stated that Microsoft would be willing to enter into discussion immediately if the new board that has been nominated were elected."

In a separate press release, Microsoft underscored Icahn's statement, adding that despite speaking with Yahoo!'s board since last year, the company decided that it cannot reach an agreement with the current board. Can you say trial balloon?

Though time is on Microsoft Corp. (NASDAQ: MSFT)'s side in its $44.6 billion unsolicited takeover battle for Yahoo! Inc., (NASDAQ: YHOO), that doesn't necessarily mean it will win the war.

The world's largest software company late Monday said -- predictably -- it was disappointed that Yahoo "has not embraced our full and fair proposal to combine our companies" and that it was "confident that moving forward promptly to consummate a transaction is in the best interests of all parties.''

You didn't have to be psychic to see that coming.

But Yahoo co-founder and chief executive Jerry Yang isn't stupid. Microsoft, like News Corp (NYSE: NWS) in its pursuit of Dow Jones & Co. is an uneconomic buyer of Yahoo. Steve Ballmer wants to make sure that Yahoo doesn't fall into the hands of the either Google Inc. (NASDAQ: GOOG) or a media conglomerate such as Time Warner Inc. (NYSE: TWX), parent company of AOL. He has already pledged to pay a 62% premium for a company that many on Wall Street believe has seen its best days.