MetaCrawler doesn't have to be expanded to take advantage of new technologies because it assumes that others will take care of that for them. Looks for home pages. You enter things about your movie preferences and it recommends other movies to you. Research topics include agents, automatic generation of user interfaces, natural language understanding, programming by example, intelligent information retrieval, adaptive hypertext, discourse planning, plan recognition, user modeling and adaptation, presentation design, intelligent tutoring, and multimodal interfaces. IUI is a pretty huge, amorphous area, with fuzzy boundaries.
Planning is a kind of search in which one constructs a course of action to meet specific goals.
In a mixed-initiative system, the user and the machine both contribute to planning without the need for a constant exchange of explicit instructions. A simple example is blocks world and getting a particular color on top. But, in the past, these systems typically did not involve users. For example, getting large numbers of people from one place to another is a logistical problem that is not readily solved with pencil and paper. They spend time thinking about the problem and various ways to solve it.