If prior to the Yahoo / Microsoft deal you were ranking Bing as the least important of the Tier I engines, you may be forgiven for that, but if you have not put Bing under closer SEO radar after the deal, you are making a mistake. Really, if you think about, the four search engines that generally make the charts, the news or capture market share are Google, Yahoo!, Bing and AOL.
from Internet and Businesses Online: SEO Articles from EzineArticles.com