Yahoo optimization is not help full to gain good result for your website.e.g. if you selling online product and you get top ten position on yahoo, so it not mean that your get good buyers for your page. The yahoo keyword tracking is very poor compare to google because google always give best result for all website. You can see while searching on yahoo the result shows any site which you not searcihng. Same problem shows on others also. yahoo have wide range of users but still somewhere down the line yahoo not giving best result for there users.
So i suggest you don't target yahoo. its tottaly time wastege of work.
I suppose yahoo does give the best serarch results. Don't know but Yahoo can be better in some lind of compare to google specific terms.Is there atleast one criteria for which you prefer using the Yahoo Search engine over Google search.
For your website, you won’t get full results with optimization for Yahoo. Unlike Google, Yahoo displays irrelevant results and doesn’t attract targeted traffic.
Yahoo is like Google in terms of counting the links pointing at websites and then evaluating their on page elements before giving them some ranks plus traffic shares. If your website's on/off page factors are very strong, after a while some top Yahoo ranks would be gained as well.