I had problems get drag&drop working in qt, so i have written my own one.
When i push a button, a timer starts and sets geometry of the button to the position of the mouse (or finger). When i release the mousebutton, the timer stops.
With this, you can make a rule that only the x or y property of the button is set to the mouse.

I use this in my app, an older sourcecode is available here:
svn checkout https://vcs.maemo.org/svn/drinkcounter