Watson by Intellext is now available in a free "personal" version. Watson conducts a search for you in the background, based on what you are currently writing or researching. From their home page:
Why go searching when you can have results found for you?
We’re changing the game. From Search. To Found. Watson understands what you are working on and brings you the information you need – from anywhere – web search engines, desktop search applications, blogs, news sites, subscription services, even your company's information systems. In real-time, without being asked. It’s like having a personal research assistant you don’t have to micromanage. Or pay for, because now Watson is available for free.
I played with an earlier version and was disappointed when the trial period came to an end - but not enough to buy it. I like that it constantly refines the search, based on what I am writing. It is able to get closer to good matches, primarily because it is creating more nuanced search strings. I can see how it can be a valuable tool for people who write and research a lot, particularly when looking for materials related to your topics of interest.
The free version will have advertising. The professional version is customizable, allowing you to hook into premium subscription services and able to search enterprise sources.
Watson were at KM Chicago in June 2005, and I wrote about it then.