There is no doubt that Currently Google is the sole internet king but for how long.
Yahoo and bing are emerging as competitors of Google currently it sounds laughable but rigorous study of the reports and trend show that there will be time when Yahoo and Bing will not only compete Google but outstand it in many fields.
In some cases it has been observed that click rates of yahoo and bing are found more then Google, The amazing thing is when your link is on top in Bing then for sure it will be on top in Yahoo so you will get dual effect.
You can call it bingahoo effect, both Search engines algorithm are adjusted in such a way that you get attention by some how nearly same on both, so there is some serious potential for publishers in Yahoo and Bing, so you should be thinking of search engine optimizing your website according to algorithm of Bing and yahoo.