I myself am interested in semantic/knowledge extraction, association, and representation. I really like the idea of concept indexing and even though there is a practical side to all of this as well, I was thinking of the value of such research to large-scale socio-psychological research where accurate generalizations of individual behavior within a group take center stage.
We're working on collocation extraction for a French dictionary we are building. I plan on using part of our corpus for categorizing lexemes according to an ontology I plan to extract from a broader range of corpora--basically using pre-existing encyclopedic knowledge to build an ontology instead of creating the ontology beforehand. I plan to use XML topic maps to do this. (I'm not even vaguely close to an implementation.)