My old boss liked 'em up. His argument was that if something metal were to strike the plug, dislodging it from the receptacle, the metal would be more likely to touch the ground prong rather than the hot, say a cat knocks a lamp over or something.
In residential, I put them in "ground down" unless the customer wants them up, simply because I've run into problems with things like night-lights, CO2 detectors (plug-in type) and appliance cords (90 degree angle type)that have to be plugged in upside down if the grounds are up.
And, most home-owners like them to look like a face...
In commercial applications, I put the grounds up unless otherwise suggested.