Sometimes in business, as in a relationship, there is time when you should yes. Otherwise, it will be too late and saying “yes” won’t mater. And this seems to be a lesson which Yahoo will learn the hard way.

After Google has turned down the advertising deal, Yahoo is turning to Microsoft, but it seems like the “yes” time has passed.

Google has officially called off its proposed advertising alliance with Yahoo following antitrust opposition from the US Justice Department.

The move was seen as a setback to both companies, but especially to the ailing Yahoo, which had hoped to book as much as 450 million dollars per year in added operating income by running Google's more lucrative ads next to its own search results.

Yahoo CEO Jerry Wang said earlier this week that Microsoft should bid for his company, but Steve Ballmer responded, by saying during a business lunch in Sydney that Microsoft has moved one.

Speaking about Jerry Wang’s comment that Microsoft should buy Yahoo, Steve Ballmer, the same man who has insisted some months ago to buy the Web giant said he is not interested anymore.

Six months ago, Microsoft has made a $47.5 billion takeover bid but Yahoo repeatedly rejected the offer.

Now, it seems like for Steve Ballmer is revenge time. “We made an offer, we made another offer, and it was clear that Yahoo didn't want to sell the business to us and we moved on” Ballmer was quoted as saying.

“They turned us down at $33 a share," Ballmer added. Yahoo shares last traded at $13.96 on the New York Stock Exchange.

Steve Ballmer said that Microsoft is still working to improve the search engine technology and there are some opportunities to collaborate with Yahoo.

Shares of ailing internet pioneer Yahoo plunged more than 10 per cent Friday. The comments sent Yahoo shares down as much as 17 per cent, to 11.65 dollars, in Friday's trading on the Nasdaq, though they later recovered to 12.10 dollars.

In the past months, Microsoft announced several initiatives regarding its Live Search engine and made several acquisitions.

For example in July Microsoft acquired Powerset, a platform for semantic search. In May, Powerset announced the public availability of its latest beta product, a search engine that delivers query results based on meaning, rather than words, delivering valid answers and improving the search experience.

The San Francisco-based company was founded in 2005 by Foundation Capital, Founders Fund and Paperboy Ventures, and became best known for the search engine they’ve created for Wikipedia articles, which tries to answer questions like “Who is” or “What is” in order to better adapt to the user’s needs.

According to Microsoft, one third of the searches don’t get answered on the first search and first click, due to differences in phrasing or context between a user’s search and the way the same information is expressed on webpages, or due to the lack of clarity in the descriptions for each webpage in the search results.

Also, last month Microsoft launched Search Perks, a promotion which awards points to regular users of Live Search. Users will be given points for every search made, with 25 daily searches to be rewarded. The points can be then exchanged for books, music downloads and other prizes. This campaign is aggressively promoting Microsoft’s search engine, taking advantage of the current economic situation in the U.S tempting people to use their product in exchange for different prizes.

The campaign is currently only available in the U.S and users’ searches will be monitored by a program downloadable in the form of a toolbar for Internet Explorer. The program supports any version of IE higher than 6. The campaign ends in April next year and those who register before the end of December this year will receive a bonus of 500 extra points. The points accumulated during the promotion can only be exchanged for prizes in April, at the end of the promotion.