One of the things I see lots of Internet Marketers doing is putting their full focus on Google and their search engine rankings, to the exclusion of all other search engines.At first glance this makes sense because Google do have by far the largest market share i.e. more people use Google for finding what they want on the Internet than any other search engine.
However because more people use it, more advertisers are drawn to it and advertise with Google, so this often brings more competition, and more cost to advertise.