User interfaces are a significant area of computers and are multi-disciplinary in their nature because they represent the trait d'union between humans and machines. As computing becomes more and more pervasive this area grows and a broader range of people get involved and affected by it.
Main areas involved in User Interface are
as pointed out by Alan Cooper in his brilliant The Inmates Are Running the Asylum: Why High-Tech Products Drive Us Crazy and How to Restore the Sanity, often the area of interface design and programming are incompatible, and we could also state the same for graphical design. Everyone of us has experienced beautiful unusable programs, or ergonomic and ugly programs, or too-many-features-packed-in-a-single-form programs.