People searching the web with Yahoo tends to have alower IQ and webknowledge, so therefore it easier to sell them stuff
Ranking high in Yahoo has done very little for me. I get a lot more traffic from Google even if I'm lower in the SERP.
Meta tags, keywords and descriptions still play an important role with Yahoo. So when optimizing your site pay attention to them.
if you target Google Ranking Yahoo and Bing will Automatically follow it's. and Google is still No 1.