Facebook & Yahoo search partnership?

Unconfirmed rumors have Yahoo! CEO Marissa Mayer and Facebook COO Sheryl Sandberg discussing a potential partnership on web-based search between the two technology companies.

If such an agreement were to be reached, how significant could it be? On one hand Facebook seeks to boost its web search facility, while Yahoo! can benefit from Facebook's over 1 billion users. Such an alliance could pose a threat to Google, but how significant that threat would be is hard to tell. And where would this leave Yahoo!'s alliance with Microsoft?

Dethroning Google, currently dominating web-search with 66% market share, would be a near-impossible mission but such a Yahoo!-Facebook alliance could definitely cause some balance shifting among the world's tech giants.  

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