Aside from a little paragraph explaining what happened, there’s not much else about it. Yahoo is now being powered by Bing search results, something that has been being worked on for sometime. This is a relationship that will likely be benefitial to both sides, mostly Microsoft because it means Bing! will be getting a part of the userbase of the Yahoo Search and will be getting money from the ads being placed.
Still, I would much rather either use Google or go to the Bing! website itself, instead of using Yahoo to show me Bing! results.
Via Bing.com Blog