A latest Yahoo! email discusses some of the organic Yahoo-to-Bing transition topics. Yahoo! confirmed of testing Bing powered results "offline," as well as "live" search results, both paid and organic, on live Yahoo Search queries, "Though much of our testing is already happening offline, this month we'll also test the delivery of organic and paid search results provided by Microsoft on live Yahoo! traffic."
Yahoo said the "testing volumes will fluctuate during this period" and they'll make sure to keep "paid search volume in particular kept low," as to not impact advertisers.
Yahoo! has also posted a video "How the Yahoo! and Microsoft Search Alliance can benefit advertisers" — Combining scale with the convenience of a single platform, Microsoft and Yahoo! Search Alliance can help advertisers reach more consumers more easily: