This week Yahoo! launched version two of BOSS (a "build your own search service"), a data API that gives developers access to web search, image and news content for a usage fee. Version one of BOSS will be shut down this summer, scheduled for July 20, 2011.
The primary changes in version two are that web and image search results and now sourced from Microsoft's search engine, Yahoo branding attribution is now required (the first version allowed for white labeling), and arguably the most significant in that developers are now charged based on query volume.
The Yahoo! Search Boss v2 API Guide can be found here which includes information on using oAuth with the new API, syntax specification on querying the API and the formats, and syntax for calling ads from the platform.