Take a look at this Youtube video- you’ll notice that many of the features Steve Jobs demos back in 1992 (according to Wikipedia) are features of Mac OS X. Certainly much has been said about Apple acquiring Next and making NextStep into the Mac OS X. But notice how so many of the features have existed in operating systems for 17 years!
But the NextStep interface is not beautiful. When Apple released Mac OS X with its evolving Aqua user interface, it put a beautiful face on some quality features- not new features, but features that most people hadn’t been willing to stare at for hours at a time. Note that some of these features are still trickling into the Mac OS X, iLife, and iWork codebases.
So what parts of your app could be more beautiful? I’m not talking about your feature set or functionality. Is it so beautiful it’s a pleasure to use? What’s the hardest thing you have to overcome in polishing the UI of a GNOME app?