Not only is Yahoo Japan dropping Google from their search engine, starting yesterday, the Japanese portal began having all of its SERP ads served by Overture. SearchEngineJournal reports that previously, Yahoo Japan search results featured ads served by other search companies, with Overture ads mixed. Now Yahoo Japan will be Overture only.
To anybody who knows anything about Yahoo Japan you will recall that they opted to use both AdWords and Overture PPC. Of course now they no longer carry the AdWords. That article made it sound like Yahoo Japan had a smorgasbord of ads from other companies.
If you see any decent articles about this switch in English let me know. There's a lot about this in Japanese.