All search engines have their own algorithms to determine the value and, therefore, positioning of websites. While the majority of SEO work tends to concentrate on Google because of the sheer weight of searches they receive it would be foolish to discount or ignore the other major search engines. Yahoo is considered one of the big three along with Google and MSN and by concentrating a little more time and effort on Yahoo optimization it is quite possible to gain a good amount of traffic. With ultra competitive keywords it may actually provide an easier way to generate search traffic than gearing all your efforts solely towards Google.