Internet powerhouses Yahoo Inc. and eBay Inc. are joining forces in an alliance that appears aimed at thwarting the recent expansions of online search engine leader Google Inc. and Microsoft Corp. Under the multi-year partnership announced Thursday, the Silicon Valley companies will draw upon each other's strengths in online advertising, payments and communications so they can connect with even more web surfers than they already do.
Sunnyvale, Calif.-based Yahoo operates the world's most visited website with 402 million users and ranks second in the lucrative search advertising market behind Google. B ut the deal between Yahoo and eBay seems likely to shift the competitive landscape.
Yahoo will become the exclusive provider of graphical advertising throughout eBay's website and will provide some search-generated ads, as well. Yahoo's brand and search engine will also be blended into an eBay toolbar that has been downloaded by four million users so far.
News source: The Toronto Star
Sunnyvale, Calif.-based Yahoo operates the world's most visited website with 402 million users and ranks second in the lucrative search advertising market behind Google. B ut the deal between Yahoo and eBay seems likely to shift the competitive landscape.
Yahoo will become the exclusive provider of graphical advertising throughout eBay's website and will provide some search-generated ads, as well. Yahoo's brand and search engine will also be blended into an eBay toolbar that has been downloaded by four million users so far.

I think that's the reason google leads the advertising scene.
Their ads are unobtrusive, contrary to those huge graphical ads that appear on the MSN and Yahoo portals/sites.
As an example, compare the news section on the three MSN, Yahoo and Google, and compare how they made use of the ads and you'll see the mess.
Don't know if I am right or not, but that's rather my own opinion.
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