I am not sure where I've seen the statistics, but the overwhelming majority of people use Google. Then goes Yahoo, then Bing, then all the other search engines. Don't remember the numbers exactly, but the difference is huge - something around 90% come from Google. All search engines have different formulas to how they rank sites, and there is nothing you can do for Yahoo separately. You do not need to pay 600 to be found on yahoo (commenting on the previous answer), - it costs $299 per year to get a good LINK from Yahoo, and this link will be counted by Google too, but you do not need this link to be FOUND on Yahoo. You need to submit your sitemap, if you are not found on Yahoo at all (that is, if you have a website). For Hubpages content you don't need to do anything.