Place entities where the mouse cursor meets the terrain

Currently when you move an entity you move the entity in the world, and mouse movements are translated to object movement. This is good when you want to have great control over where you place the entity, but not so good when trying to quickly place something. For that it would be better if you moved the mouse cursor just as normally and the object is placed where the cursor meets the terrain. By pressing and holding a button (ctrl?) the old placement mode could be enabled; but the default should be to use mouse-to-terrain.