UI UI UI

What is the definition of a good user interface? The problem for the product company is that good UI for sales users is not the same thing as a good UI for the day-to-day users. With us working with an application for Windows Mobile, this is a big issue. When my company started working with mobile application, the mere showing the business data on the hand held guaranteed that the application was good from a sales person's perspective. But today, with IPhone and HTC Touch, the sales persons and the person's doing all the purchases expect more. It's supposed to look zazzy. Modern. Iphonish. And a nice looking application is important. I look things that look nice and if I work with a program with poor colors, and old fashioned style, I tend not to like the program.
But we also have to think about the users. And then I don't mean sales persons using the application for short sales presentations. I'm talking about the user's who are dependent on a good user interface for their daily and critical work. Of course they want it nice looking. But if that means three more clicks on a more than daily routine, they will soon grow to hate that UI.
It will be interesting to follow how the UI of Microsoft Office after version 2007. I hated the ribbon from start. But I've learned to accept it. But what I can't accept is that the implementation of the ribbon has increased my daily manual work. And I hope I will remember that during the coming months, when the UI for our mobile application will be stabilized.