Tag-based searching

When I teach EAD, I stress the value of tagging as a way to add intelligence to the text.  Yesterday I got this question from a student:

"We're doing all this encoding in part so that search engines can search these documents better and understand when Washington is a city or a person's name.  What kinds of search engines are we talking about?  Not Yahoo or Google.  Can you give us a demo of one of these search engines?"

I know that the Women Travel Writers Project set up tag-based searches in DynaWeb, but they've gone away.  Does anyone know of others?

Elizabeth H. Dow
Associate Professor
School of Library and Information Science
Louisiana State University