I'm on OSX 10.9. With lwjgl-2.8.5, Display.setLocation worked fine, but with lwjgl-2.9.0, it has no effect if the display has already been created. I looked at the code, and MacOSXDisplay's reshape method (https://github.com/LWJGL/lwjgl/blob/master/src/java/org/lwjgl/opengl/MacOSXDisplay.java#L351) is just empty.
Related to this thread (http://lwjgl.org/forum/index.php/topic,5278.0.html). There's sample code there.