Hi there,
It would be a miracle, if there was an option to drop a 6 poly box in the 3D view and move it around. The only adjustable parameter being it's x,y,z dimensions.
With the size of the box being user defined, we can finally have an excellent sense when we are creating mountains, roads, rivers, erosion etc. This is really fantastic to have a box with the size of a human or a car (or anything I'd want to fit on certain places) so I can directly move it around, rotate it like I'd do in 3Ds MAX. Basically, this feature helps to create more game-play friendly terrains by having an excellent sense of scale when we are looking at the terrain in 3D view.
Sense of scale has always been a big issue to me, specially since I create maps in various sizes.