Microsoft and Yahoo announced this morning that they've reached another big milestone in their search partnership, completing the integration of Yahoo advertising customers' accounts into the Microsoft AdCenter platform in the U.S. and Canada. That means Microsoft's system is now powering all of the search ads across Yahoo and Bing in the two countries.

"Mission Accomplished," says Yahoo's advertising blog.

The combination of the two platforms has given Microsoft around 30 percent of the search market in the United States, promising more of the mass it needs to deliver relevant results to searchers and a larger audience to advertisers. Microsoft says the combination will create a "competitive alternative in search," letting advertisers reach 163 million searchers in the U.S. and 15 million in Canada.

Microsoft is hoping the alliance will put it in a better position to compete more effectively against Google.

Yahoo says it will keep making improvements to its own search user interface, while turning over the underlying search engineering to Microsoft frees the company up to focus on other things.