they look very good.  use raytraced sun to get shadow edge blur. no blur on shadow edges next to the object casting the shadow, then the blur increases as the shadow edge gets farther away from the object.  bill did a cloud procedural for the sphere, but it has hundreds of nodes IIRC.

p.s. I just checked outside and the noon shadow edge had a blur width of ~1 cm at 1 m, ~3 cm at 3 m, but it may not be linear. hence it would only be obvious in relatively close shots.