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

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.

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. 

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

No, my main focus has always been on Google, never enough time in a project to focus on smaller gains like Yahoo/Bing (which are mostly the same engine, these days).

If time permits targeting other search engines, then efforts are usually placed on Yandex.

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.

Yes, All the search engines have their own algorithms, based on there algorithm update we need to change the strategies.