In the news section on standard software in the Germany IT magazine IX a Forrester Consulting survey was quoted that provides some evidence that UIs matter. . The survey states that for over 80% of CIOs and heads of IT departments the user interface is critical when they make buying decisions. (photo of the article is from IX 2008-01)
The IX magazine is typically more technically oriented and I think little article underlines a trend that happens: people responsible in IT realized how vital the interaction between users and systems are. In my eyes optimizing the user interface is in many business applications the “low hanging fruit” to optimize efficiency and eventually ROI.