I recently tried this and, while my knowledge of C++ is not exactly that great, I found it to be pretty un-Mac like. It seems to support many things including sheets but other things remain totally foreign in the interface. I think you will get similar results to Java Swing or SWT using QT. So competing with the Cocoa apps out there will not be easy.
Google Earth for the Mac is the only app that I can think of which uses QT.