I recently needed to "grey-box" something - I needed to check the flow from use-case to use-case throughout the app. Rather than use the standard flex themes, I used Juan Sanchez's "Shadow" theme.
Usually we think of themes and skins in terms of final product - at least I did until about a week ago - but there's a call for their use in any situation. What impression do we give our audience about the product? What are we communicating about our attention to detail, our understanding of aesthetics, and what first impression are we inspiring people to infer, or feel?
I plan on using more themes as different situations arise, and I use "Obsidian" for my own personal tools just because I like it & it feels good to me. And of course content and functionality need to be high-quality, but I've found that in many cases there are more than a few people in a room who, when asked why they went with our product (back a few months ago when I had a job) was that "it just felt right". Hm. Not an answer Descartes would be happy with, but a valid and valubale answer none-the-less.