This is something that has been discussed a lot over the years, and I have devoted a lot of thought and analysis to it. There are two aspects to the UI design, first is "prettiness" and second is "usability".
Prettiness shouldn't be discounted as frippery it is important and we have always struggled getting people to take the application seriously because it just looks old fashioned. I have said many times over the years it would be great to get a professional UI designer on board to tell us how it should look. As a designer I make a great accountant
Usability is something I have studied a lot. In most of Africa, English or French is the language of business, but isn't the first language of many of the people. This means the users are using an interface written in their second or even third language, and when we are training them they frequently look bewildered at the options available. Many of the fields available simply don't apply to them, and serve simply to confuse. I did experiment a while back in making the screens configurable, so that it would be possible to only show options that apply to that user. This used JavaScript but the problem was that the changes to every script were just too much. I recently had a discussion with an Indian developer who was also looking into making webERP do this. The problem is how to do this without really invasive changes to every script. I had an idea of doing it via custom css files but not had a chance to progress this idea.
Tim