If I'm not mistaken Yahoo Japan is one of the last properties using Yahoo's Overture platform, which started out as GoTo. This is still used in Asia, but these departures in the Korean market are going to have a big impact.
NHN Corp., owner of South Korea’s largest Internet search engine, will discontinue using Yahoo! Inc.’s online search-advertising service and replace it with its own technology.
NHN will use its Click Choice service after the company’s contract with Yahoo’s Overture Services Inc. expires in the second half of this year, Seongnam, South Korea-based NHN said in a statement today. Chief Executive Officer Kim Sang Hun said the Korean company “desperately” needs a more flexible system that’s suitable for Korean advertisers.
The move is a blow for Yahoo’s business in Asia’s fourth- largest economy, where NHN’s Naver search engine controls an estimated 65 percent of Web queries.
Not the last to use the platform Daum is still using it. They haven't announced what they will do yet. Daum switched from Google platform to Yahoo last year but the Microsoft Ad Platform is not used in Japan or Korea so I think it's a hard sell.
I've never heard anyone from Yahoo Japan sales team or the Yahoo seminars mentioning that they outsource the Panama platform to Korea. Both countries licenses Overture Panama platform from Yahoo US from my knowledge. In Korea it's still Overture Korea. They could be a major stakeholder though.