When developing business applications the main focus is on application, business and database logic as well as complex business and IT processes. But what about the GUI which is the interface between user and application? From the user's view it's the main point of contact and an important part of the application when testing if requirements are fullfilled.
From the developer's view the importance of the user interface tier is often underestimated. Be honest: Don't you think that it's just that easy? Putting some buttons, fields, text and ready-steady-go? Yes, it can be easy. But if the complexity of the application grows, it is usefull to care about an elaborated and intelligent GUI which supports the user processes as well as application processes. Try to make a good deal between application complexity and user's requirements.
So it's about user interface design,too. "Design" - in this case - does not only mean playing around with colors and forms but dealing with the advantage to find the best possible way to provide an understanding between user and application. "Form follows function" means "Form supporting function according to the customer requirements" (and not that the form is less important compared to the function).
The user / customer has another point of view onto the application compared to the developer: In his eyes, the application consists of what the display shows and how "it" reacts on the user's input. So the UI has to understand the user, not otherwise. (And corresponding to this point of view the customer mostly communicates his requirements, but that's another topic)
Therefore it's usefull for a project to integrate the role of an UI (User Interface) Engineer who connects the user's expectations and the requirements of the application logic with the use of UX (User Experience) / UI Design Patterns:
Further reading on "User Experience Design"
The Five Competencies of User Experience Design
Focusses on: Software Engineers
Presentation Layer Design Checklist
Focusses on: Requirements Engineering
Several great slides about UX in the web
Focusses on: Web Developer