Announcing the testing of Panama, Yahoo's contextual search advertising platform in UK, the letter said, "We constantly test new implementations and matching technologies. To help ensure we launch our new ranking model successfully we have started running a limited test across our UK advertiser listings in which the display order of Sponsored Search listings in some keyword markets is based on factors other than bid."
The date is tentative though it will probably happen in the 2nd quarter. "Our new Sponsored Search system will be rolled out in the UK soon, beginning with advertiser migration later this quarter. We will be contacting you with more specific information as the rollout date approaches."
The complete mail detailing Yahoo! Panama's launch in UK can be read at PPC.