Couple of things I found out that helped porting a QT application to Mac:
The QMainWindow you create does not look like a native Cocoa window. The status bar is there, no matter what you request, the menu doesn't port and the icon is yucky.
Here's what you can do:
Remove status bar/resize grip:
Don't show unneeded icon in the title bar and move a QAction to Mac's main menu:
