Do you use separate Seo strategies for Google,Yahoo and Bing?

No, not generally. Bing is still a tiny, tiny percentage of search traffic. Don't trust the Comscore data - they have a lot smaller market share.

Yes. Google, Bing, Yahoo - all have unique algorithms to produce their SERPs. Each has a different way of weighing the factors responsible for a site's ranking and hence would need a different SEO strategy. Trying to rank on all3 simultaneously could take some gruesome work.

Yes I use separate strategies for Google,Yahoo and other search engines.More backlinks are required for Google .It pays more attention to backlinks and site authority while Yahoo and Bing pays more attention to title and Meta tags. Hence, a site takes time to rank on Google as compared to Yahoo and Bing.

Yes , As google work on content and yahoo and bing works on key words

There are no separate strategies for Google, Yahoo and Bing. You will need to follow the same techniques with good optimization techniques to help rank your website in all search engines.

I believe that all platforms have their own algorithms and it would not serve well to focus on understanding those. Instead put energies in the creativity of your content, make it more engaging and remember-able instead of getting lost in the number game. 

I would target google as google holds around 77% of the search market. 

Yes I use separate strategies for Google,Yahoo and Bing.

Not my field. And I have deep misgivings over reliance on SEO to solve marketing issues. Coomon sense that is then applied tpo SEO will do it:-)

As each of them, has a different algorithm, you should separate your SEO strategy. You should concentrate on google because it privilege content instead of key words, and it monopolize the majority of the traffic.