With many people using search engines to navigate the web, search engine optimization (SEO) has quickly become integral to the operation of online businesses. According to recent search data published by Nielsen, Americans conducted more than nine million searches in April alone.

Overall, total searches were down from March by nearly 700,000 searches, but were up from last April by almost 400,000. Google is still the most popular search engine, accounting for 5,920,554 – 65.1 percent – of searches. Year-over-year, the search engine is up a percentage point, but it’s down in total market share from March.

Bing also continues to grow, much at the expense of its partner, Yahoo. Year-over-year, Microsoft-run search engines have increased their market share by 3 percent, while Yahoo was down 3 percent. From March 2010, Yahoo did gain 0.1 percent market share, while Bing gained 0.7 percent.

Last year, Yahoo and Microsoft entered into a 10-year agreement in which Microsoft’s search engine, Bing, would power Yahoo Search. In return, Yahoo would take care of all the advertising arrangements for the two search engines.