One of the papers released to the past Conference on Information and Knowledge Management was Y!Q: Contextual Search at the Point of Inspiration by Reiner Kraft, Farzin Maghoul, Chi Chao Chang from Yahoo (8 pages, PDF).
From the abstract:
This paper presents Y!Q—a first of its kind large-scale contextual search system—and provides an overview of its system design and architecture. Y!Q solves two major problems. First, how to capture high quality search context. Second, how to use that context in a way to improve the relevancy of search queries.
The paper is a real interesting read – especially the sections describing how Y!Q determines context. Everything is pretty high level so no juicy details on how Y!Q specifically works, but a good read anyways.