This is fact that yahoo is good for SEO. but I don't Think so... Google is much better than Yahoo... And i do use only Google...
Next to Google, yes. But people still go to Google. I remember Yahoo search used to be powered by Google search. Can't remember when exactly.
I believe google is the best search engine for SEO. yahoo also not bad but we can not compare with google search engine.
It is natural for you to get yahoo links into your website, which is indexed by Google. You would have to become an active member of yahoo answers in this case.
Google is best, but it is way easier to rank in Yahoo. I had a site number 1 in Yahoo for Facebook Marketing while I was still on pg 2 for Google. Yahoo gets less traffic but it is best to be ranked across several SE's for the best effect.