By the way, since this thread started with Ruben's post about
    the wiki page he updated:

       http://qt-project.org/wiki/MinGW-64-bit

This wiki for building Qt-5.x.
 
    it might be relevant to note that there are two other "wiki"
    pages pertaining to Qt and MinGW:

http://wiki.batcom-it.net/index.php?title=Building_Qt_on_Windows_(MinGW)
http://qt-project.org/wiki/Building_Qt_Desktop_for_Windows_with_MinGW

And this for Qt-4.x.