Bogdan, if i render your scene it's ok. If i make a new scne with the same material it don't work. I don't find a difference between your file which is ok and my file where it don't work. Hope you find the reason why it don't work by me.
I found the problem. Your plane has motion blur on and displacement is not working with motion blur.
In object properties, the rendering control, display properties and motion blur were controlled by layer. Uncheck the button on all three and make it "By Object". Then, on Motion blur group, make it none.
Last edited by Bogdan Coroi on Fri Jun 27, 2008 1:23 am, edited 2 times in total.