Okay. Great. You rank #1 on Yahoo. But for what keyword? Is it a highly competitive one-word keyphrase or some uncompetitive five word keyphrase?
And what do you do with that ranking? Let it sift through and leave or convert to your customers? Converting attracted customers is easier than attracting new ones. Continue working on your site content, improve site usability and accessibility to convert even more customers
That being said, Yahoo has different demographics from Google. Google has more tech-savvy folks and I am not sure for Yahoo. The rest of the pack? (That being said, MSN does have more non-Internet savvy folks like mom, mom, teenagers, etc)