Ofcouse yahoo and bing don't have PR systems, Google Rank based on the quality backlink, content and optimization parts Yahoo and bing depends on the backlink.
Yahoo and Bing do not rank pages based on backlinks. It is only Google and also note that Yahoo and Bing are yet in beta and so very little experimental SEO can be said about them.
Hi My personnel experience says that if you go for optimizing for google then the other search engines like yahoo or bing there also your site will get optimized partly. No one knows the proper algorithm or the procedure used by any search engine. Its their secret. We can only predict how to optimize. There are many ways to optimize.
