I know this is a subjective thing, but I think the app's graphical style is somewhat ugly. If I'm supposed to be creating an attractive animation for my site, I want to be surrounded by a similarly attractive workspace. I know it's a nitpick, but it's why I write code in Coda, not Vim, TextMate, BBEdit, or anything else. I'm fickle like that.
I see what you mean... The trouble for me is that I'm working on Radi alone. Coming up with an attractive custom UI style is a big undertaking with an inherently uncertain result.
It feels like a safer use of my time to work on features, and just aim for a "boring but reasonably professional grey" appearance for the interface. I know that many artists actually prefer grey UIs so that it doesn't compete with the actual content.
I've tried to use Cocoa-native controls wherever possible, and that also limits the UI possibilities quite a bit. The overall look needs to be rather neutral so that changes in the Aqua look don't mess up the custom-drawn controls. (Recently Lion had a big change in most of the standard controls' appearance, but IMHO the updated look made Radi look a bit better.)
