Just to see how easy it is to port Qtopia/Core to other platforms, I gave Qtopia/Core on Mac OS X a try. A few patches later:
The example is not using any Mac OS X libraries to draw. Instead, it uses shared memory to communicate directly with qvfb, Qt's virtual frame buffer. The virtual frame buffer is a native OS X application, built with Qt/Mac. It simulates an embedded device that doesn't have a windowing system. So now, you have three options to run your favourite Qt application natively on the Mac - Aqua native, Mac/X11 and through qvfb.