ResourceShelf discusses a new toolbar application called Seruku. "Seruku is toolbar-based application that ... makes a copy (called a snapshot) of every html web page you've viewed in your browser, stores it locally, indexes the content and then, when needed, allows you to keyword search the full text of this material."
My first thought was that this is silly, basically reimplementing the browser history and cache with a search layered on top. But then I realized that this really could be useful. Wouldn't it be nice to be able to do a Google search that was limited to web pages you have seen before?
It may just be a matter of time before Google puts this functionality in their toolbar, since this is an easy extention to their upcoming search of your hard drive.
Update: John Battelle briefly compares Seruku to Furl.
Update: Microsoft Research's "Stuff I've Seen" project is a generalized version of Seruku.