We are google marketers. We evaluate our performance according to Google results. Google is the most used search engine itself dominating more than 70% of the market share! Ofcourse your site will definitely benefit on all other search engines too, but we only take google as a measure to assess our performace.
Currently Google search results also show up on google's partner sites such as AOL, Yahoo, Netscape and thousands of others. So if your site ranks on top on google, it also ranks on top on all these engines.
