Yahoo users (in the U.S. and Canada) will start seeing Bing results for organic searches this week. Yahoo and Microsoft announced that the transition is starting, and that the paid search transition is in the middle of testing.

"Later this week, we will begin the work of transitioning the back-end technology for Yahoo! Search over to the Bing platform," says Yahoo. "This is an important step toward our goal of improving the overall relevance of Yahoo! organic search results and attracting a larger audience to Yahoo! Search, to ultimately put your ads in front of more potential customers."

"Soon, you’ll be able to access a transition portal from within your Yahoo! Search Marketing account," the company adds. "This portal will walk you through the simple step-by-step process of creating a Microsoft Advertising adCenter account and importing your campaigns, or linking an existing adCenter account that you may already have."

The portal is currently being tested with a limited number of accounts. Users will be emailed when it’s available.

Yahoo still intends to have the transition in place before the holiday season, but may elect to wait until 2011 if they feel like that would improve the user experience.

"Once this organic transition is complete, Bing will power 5.2 billion monthly searches… that’s 31.6% of the search market share in the U.S. (290 million monthly searches and 8.6% share in Canada)," says Microsoft’s Tina Kelleher, referring to comScore data (more on that here).