An intelligent user interface can watch what the user does and do the same thing, by example. For example, A system called Tiger watches mouse clicks, etc. SAGE, a suite of systems, builds visualizations from data, automatically. Jim Foley worked on UIDE, a general environment that assists you in building interfaces. It contains a knowledge base, and could either critique what you did, or jump in and add to what you were doing.
Agents are really only a small part of intelligent interfaces.
HCI techniques alone are inadequate. AI techniques alone are inadequate. A synthesis of AI and HCI can be effective. AI is really about search and knowledge. How to manage knowledge representation and how to search through it effectively.