Google insights has interesting data on the geographic origin of web search volume for Bing
The prevailing wisdom was that Bing would take share away from Yahoo. However region interest for Bing is the highest in China followed by India, the US, UK, France, Canada, Spain, Germany and South Africa in a decreasing order of interest.
The market share for search in China is dominated by Baidu. Google is a distant second and Yahoo a distant third.
Google is leader in search in India.
So should Bing worry Google more than Yahoo