The partnership between Yahoo and Microsoft is finally coming to fruition. The companies announced today that the "transition of organic search" is finished, with Bing powering Yahoo's web, image and video searches on both desktop and mobile devices in the US and Canada (English only for now). The shift is planned for additional markets as well, but we haven't seen a detailed timeline.

With the initial phase complete, Yahoo will presumably focus more on refining its offering as a web portal, instead of investing heavily in its search engine technology. Meanwhile, Microsoft says the companies are working on the migration to adCenter, which is expected to be done sometime this fall. "Our primary goal is to provide advertisers with a quality transition experience in 2010, while being mindful of the holiday season."

Based on current estimates, Yahoo and Bing represent a combined 28% of the search market -- far less than Google's 66%, but the merger should still provide more competition to the big G. What search engine do you use, and for the loyal Yahoo users, are you bummed about the move?