Why does dragging a space in Spaces lag awfully?
Mine is slow too. Note that it works with the mouse, not the graphic, so you can click, drag, release, and move out of Spaces, and the effect will have worked, even if the graphics didn't finish yet.

Also, dragging an empty space is, for me, much faster, so if I want to swap an active work space with an empty one, it is better to drag the empty to the active than the active to the empty.