The Yahoo! Search Marketing blog have posted more information about an important change to the way ads are ranked. This confirms that the quality score update will only be active in the US from Feb 5th.
“In search advertising, user satisfaction and advertiser value are two sides of the same coin. To help create a better experience for our users and help encourage you to create better, more focused ads that are more appealing to your potential customers, we are changing the way that ads are ranked in the U.S. market. Ads in search results will be ranked by both bid amount and ad quality. This change, which will impact all advertisers, is designed to allow you to focus less on competitive bidding and more on the quality of your ads. By improving the quality of your ads and making them more relevant to users, you may be rewarded with a better ranking and reduced cost for your ads.”