Power of UI

When i was writing my "Exploring Ajax" article i mentioned a little bit to user interface. But then i delete one paragraph to make article more consistent. I do not want to throw that paragraph to trash.
Here is cut statements:

We need to ajax. We need to prevent post backs. We need to simplify user interfaces. Users should use project willingly by ease of use. I know some user interface developments are more valuable than complex business processes. Users do not see back end of the program. They know what they see. I remember we did a complex algorithm for a program. It was very hard indeed. We worked many weeks. Unfortunately users were not satisfied.

One day i changed icons on the screen. The project was transferred to us from another development group and they had used some ugly icons on the toolbar and menus. When users saw new clear icons they thank to us and started to use program and gave their feedback. Indeed program was working. But they did not want to work on it before. So they did not make tests and they behave like program had problems. It was a good experience for me.

No need to argue on power of the UI :)