[Shamanmuni]

VLC, Scrivener, Skype, Spotify for Linux; I think they all qualify as quite usable applications.

On the other hand, in GTK you have GIMP and Inkscape, which aren't exactly an UX expert's dream. In Qt you can find similar counterparts in Krita (specially Krita Sketch) and Karbon, which I think are much cleaner.

I hope they help with your preconceptions.