1) There are five major approaches to product design: user-centered design, activity-centered design, data-driven design, systems design, and genius design.
2) While user-centered design focuses on understanding user needs, all design approaches rely on the skill and judgment of the designer.
3) Different design approaches are better suited for certain types of problems - for example, activity-centered design is good for refining task flows while data-driven design is best for incremental improvements.