When dragging a window using programmatic control or animating it using a timeline the movement is not smooth. It is very choppy and appears to stutter, as if the window is oscillating slightly between two different locations. For an example of this behavior look at these two samples with JavaSE 6 update 10:

Click on the saucer to start it:
http://jfxsamples.sfbay.sun.com/FlyingSaucer/description.html

Drag the player out of the browser, release the mouse, then click to start dragging again.
http://jfxsamples.sfbay.sun.com/DraggableMP3Player/description.html