Some encouraging news for Microsoft today in its uphill climb against Google. The combination of Microsoft Bing and the Bing-powered Yahoo search engine rose to 28.48 percent market share in the U.S. in February, up from 27.44 percent in January, according to the Experian Hitwise research firm.

Google, meanwhile, experienced some rare slippage, dropping from 67.95 percent in January to 66.69 percent in February, the stats show.

And then there’s this interesting factoid, from the Experian Hitwise news release: “Yahoo! Search and Bing achieved the highest success rates in February 2011. This means that for both search engines, more than 81 percent of searches executed resulted in a visit to a Website. Google achieved a success rate of 66 percent. The share of unsuccessful searches highlights the opportunity for both the search engines and marketers to evaluate the search engine result pages to ensure that searchers are finding relevant information.”

February numbers from the comScore Networks research firm (which are the official measure of performance designated by the Yahoo/Microsoft search partnership) have yet to be released.

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