I often have difficulty convincing people that the layout/design/visual-styling of an interface has impact on how the user feels about the product as whole. All to often the argument is that the user doesn't care about those kinds of things, they just want to do what the have to do and that's that.
While I do agree that users typically use your software as a means to an end and not to sit there and admire it, I strongly feel that the design impacts the overall opinion of the software. If poorly designed, it can make it feel clunky and annoying. When designed well, it can make it feel sleek (sometimes even make it appear to perform faster) and add to an overall pleasant experience.
Keep in mind that I am in no way advocating that the design should take precedence over the usability or functionality of the interface. I am simply taking it that extra step and making it more professional and visually appealing. So once again:
How can I convince someone that the visual layout/design of an interface has a positive impact on the user experience?
(In my particular situation, performing my own user testing and feedback is not really an option, so I would appreciate answers that do not involve running my own testing)