On the heels of it's recent SearchMonkey announcement Yahoo! has released BOSS which stands for "Build your Own Search Service". BOSS allows developers to quickly plug search data directly into their application by leveraging a set of very lightweight web service calls. These two releases send a strong message that Yahoo! is backing up it's message of opening up it search system to developers.
The next version of the release, BOSS Custom, will allow developers to post data into the Yahoo! Search platform via similar web services. The concept, in my opinion, is for Yahoo! to attract developers to place additional content on it's search platform and using an open interface to benefit from more robust data collection (ie social site data, unsearchable properties or maybe...hum, properties that would like to be searched by Yahoo but no on else).
Who knows where this will go but when you are losing market share hand over fist it doesn't hurt to try and shake things up.