Speaking of Bing, we found them to have 95% similar SERPs to Yahoo at the moment for our target keywords. We rank exactly the same on Bing as we do on Yahoo, with exactly the same SERP listings. The only difference is that Bing took a few months longer to start showing our sites, and that it is sending us over 3 times less traffic than Yahoo at the moment.
I think even Yahoo matters because it may be not as popular as Google but yet is one of the best search engines and every one has to agree with this.
Search engines will give you a lower ranking or even ignore you if your pages are that badly written and do not include enough information. I also recommend making sure your website is cross browser compatible, using a tool like Multi-Browser Viewer or similar.
Backlinks, true. And yahoo is finding them easier than Google in my opinion. And all my websites are ranked higher in Yahoo, than Google But still no traffic :X
Understand the differences between them is important. Basically, Yahoo likes all of the things Google used to count as being important before Google decided that too many people knew this and were making the most highly optimized websites show up at the top instead of the most relevant sites. Bottom line: You could say that Google likes off-page factors (i.e. links) and Yahoo likes on-page factors. That's an over simplification, but it is a good rule of thumb.
For Yahoo , we should add more keywords in content. Yahoo like keyword spam a little more compared to Google. Never avoid link building. We cannot rank well without link building.
target your keyword in title tag, you will be top, according to my experience, yahoo preffer title tag most. try it
Now for the SEO's it will be a double treat. If they rank in Bing, they will rank in Google as well as both search engines are using the same Bing algorithem for Search. So instead of doing research on Yahoo, better check Bing policies.