According to research firm Nielsen, Microsoft’s Bing search engine has overtaken Yahoo! as the second most-used search engine in the United States. There is, however, a little catch. Nielsen’s numbers, which are for August of 2010, only count what they are calling “intentional searchs” and do not include contextual or slideshows searches. The company pegs Yahoo!’s U.S. search share at 13.1% and Bing’s at 13.9%; Google is still dominating with a cool 65%. To further cloud the waters, comScore’s data — from July of 2010 — shows that Yahoo!’s explicit search numbers are six points higher than Bing’s. For the time being, all we know for sure is that Google has almost two-thirds of the U.S. search market and either Bing or Yahoo! is in a distant second.