Looks useful...

Aesthetics aside, it should blend in. I think that is what makes it look good, or not. Unless all applications on OSX use X11 style, I would call the ones that do ugly, and similarly I call the stupid iTune on Windows butt ugly, or almost all Java GUI applications (well I like Eclipse). One more reason to use Qt for the GUI, then by default it blends in the native OS (although one can usually select other styles on command line)