Microsoft’s Bing search market share grew again in the United States during the month of April.

The software giant’s “decision engine” now has 14.1% U.S. market share compared to Google’s 65.4% according to data from comScore. Bing rose by 0.2 percentage points in April, a rise of 2%. Yahoo’s market share also rose slightly in April at 15.9% following a 15.7% figure in February. Microsoft’s Bing search has increased its share consistently over the past six months. Bing grew faster in October than Google and has continued to rise recently. Bing reached an all time high of 11.8% market share in November but has improved upon the figure between December and April. Microsoft’s Bing search volume increased by 29% during 2010 according to comScore. ComScore says the US search market rose by 12% last year. Experian Hitwise also named Bing UK as fastest growing search engine in March recently.

Steve Ballmer, Microsoft CEO, compared Bing to a weed in January. “We bet on Bing and are growing like a weed in that business. So I feel pretty good about the bets,” said Ballmer. The comparison of Bing to a weed is a rather accurate one. Microsoft has shown it isn’t afraid to ensure Bing is everywhere. The software giant has pushed two minute video demos of Bing on iPhones, released Bing iPhone games and ensured Bing is making its way to the latest Toyota line of cars. Microsoft also introduced a specialBing for iPad application earlier this month. The constant iteration and product updates also keeps Bing high in the mind-share of users. Microsoft appears to have followed Google’s approach with a number of UI and feature enhancements in previous months.

Google isn’t happy about Bing’s approach however. Google kicked off a search engine war of words in February after Search Engine Land posted a broad investigation into what Google claims is Bing cheating search results. Amit Singhal, a Google Fellow who works on the company’s search engine ranking algorithm, claimed that Bing was simply copying Google’s results. Google allegedly caught Microsoft’s copying by creating a “Bing Sting.” The search giant created one-time code that would manually rank a page for a certain term and create around 100 synthetic searches searches that hardly anyone would ever enter into Google. The searches returned little or no results on Google or Bing but Google created a special honeypot page to show at the top of each synthetic results page. The result? Bing started listing the random queries only a few weeks after Google began listing them.

Microsoft was quick to deny Google’s claims with a blog post entitled “Thoughts on search quality.” Microsoft’s Harry Shum simply shrugged off Google’s claims as part of over 1,000 different signals and features in Bing’s ranking algorithm. Google wasn’t happy leaving it at just that though. Amit Singhal published a Google company blog postentitled “Microsoft’s Bing uses Google search results—and denies it.” The blog post outlines much of the original report from Search Engine Land but also called Bing’s search results stale and a “cheap imitation” of Google results. Microsoft and Google employees also traded jibes over Twitter regarding the findings.

Microsoft’s search alliance with Yahoo appears to be paying off too. Marin Software, a paid search marketing platform provider, and Razorfish, an interactive marketing and technology company, unveiled the results of an exclusive study last month conducted to analyze the impact of the Search Alliance on paid search campaign performance. The results showed that the Search Alliance has resulted in improved traffic quality for advertisers and increased its share of paid search impressions by 4% and its share of clicks by 2%.

Bing also passed Wikipedia on Compete’s list of the top 50 websites for December 2010. Bing took the sixth spot with 79.8 million unique visitors. Compete reported that Bing closed the year with a 105.36 percent increase in unique visitors — the largest yearly growth among the top 50 sites.