Yahoo is Bing, but is it really?

[Maddy]

We know Yahoo results are now powered by Bings database. But what we see are not often symetrical results between the two still. While yahoo is using bing data, things are different in the returned results.

What is yahoo/bing doing differently in the yahoo results to make them differentiate their results from the Bing results?

And what can we as SEO's use to our advantage to make sure we rank equally well in both results?