Aaron Wall has written a thorough and unflattering overview of Yahoo search traffic following the release of search numbers that show Yahoo gets well over half its search volume from its partners.
Aaron discusses how this impacts arbitrage and motivates poor quality. Though possibly just a little harsh, it is worth reading and keeping in mind.
Recent numbers from Efficient Frontier show that Yahoo has nearly three times more search partners than Google - funny given Google has over three times more search volume. And as Aaron notes direct search converts "nearly twice" more than partner search traffic.
Not good numbers moving forward in a battle for the search industry. But I always managed to convert Yahoo traffic at a better CPA than Google in the financial vertical. So maybe there are niches where Yahoo benefits from its partners.... will have to keep track of this one.