From what I observe Yahoo and Bing favor DMOZ and Yahoo directory listing (conflict of interest? ha). They also favor onpage factors heavier than Google which means your url structure, meta information and onpage content/interlinking needs to be correct, unique, and relevant.
I also observed that yahoo and bing are focused more on on-page factors. After I do on-page optimization on one of my sites and get it indexed by these search engines, some of my keywords are ranking high already without doing much link building yet.
All search engines are based on optimization of page and backlinks. These are main factors but search engines have some smaller factors and it can be changed for each of them.
Yeh, Yahoo puts more importance to On page optimization factors .Bing does a mix of both Google and Yahoo strategies,however my research shows that Bing nowadays is moving towards links diversification as Google
Ranking on Yahoo has always been much easier for me for some reason, but most of my target audience would not be using Yahoo anyway.