'Over the past four years, Google has dominated the search scene. Up until last year, Google fed results to most other search engines including Yahoo, which fed some results to MSN. This outward pollination of search results made Google responsible (directly or indirectly) for over 80% of search results worldwide. After Yahoo and MSN developed their own proprietary search tools, Google's influence dropped to 54% of search results as measured in the May Nielson NetRatings survey. Following this trend has led SEOs to start paying more attention to Yahoo and MSN both of which can deliver significant chunks of search engine traffic. Search Engine Watch regularly publishes stats about the major search engines.

All search marketers know there are several search tools delivering traffic to commercial websites. While Google is the largest of all, it is important to get placements across numerous search tools. Though there are hundreds, if not thousands of search tools working on the web right now, less than ten of them provide enough traffic to be considered statistically relevant to SEOs and SEMs.'