Bing Search results are what you're getting if you are a Yahoo user in U.S. or Canada. In a blog post Satya Nadella, senior vice president of Microsoft's Online Services Division stated, "So far, Bing is only powering results in English in the U.S. and Canada, with other languages to follow in the weeks and months to come".
It's also worth noting that at the bottom of search results will now say. "Powered by Bing" for searches using Microsoft's results. Yahoo still hasn't made the transition to Microsoft's Ad Center a self serve search ad platform. Nadella also stated via her blog, "As we have said all along, our primary goal is to provide advertisers with a quality transition experience in 2010, while being mindful of the holiday season".
Yahoo should have integrated by October. The company stressed they would not be rushed into the transition however.