In the electrical world, worrying about plug orientation makes about as much sense as the Captain of the Titanic worrying about the placement of deck chairs.
It's far more important that it BE there ... AND be connected to a good path back to the service.
Personally, I like the traditional "Mister Smiley" placement. I also like the upside-down placement for switched receptacles.
Most important, though, I like to place the receptacle so as to cause the least strain on the plug. I really don't like to see an 'angle' plug with a sharp bend in the cord. The situation most often comes up with ranges, dryers, and air conditioners - though vending machines are also an issue.
With those situations, we're not really talking about receptacle orientation; we're really just trying to make up for poorly placing the receptacle in the first place.
The person who adamantly argues for a particular orientation is often the same person who places receptacles to "code minimum," customer comfort be damned. Hence, all those contorted plugs behind furniture.
Job specifications will often call for a certain orientation. While I have no objection to the specification as such, I do shake my head at the implied micro-management. It's almost a warning that some unqualified engineer type has assumed instant expertise, based on nothing more than the arrogance of a job title.
I once read through a similar discussion somewhere on the web. One individual was in favour of the pin being down. He tried to rationalize his preference by stating that if the receptacle is in that orientation and the cord end starts to pull away from the wall in a downward direction that the ground pin would be the last to lose contact.
I personally install the receptacle in whatever direction makes most sense. If I know that a certain piece of equipment will be sitting in front on a permanent basis and the manufactured cord end has a 90 degree then I might orientate the receptacle to best suit the way in which the cord can be tucked in back without getting in the way or putting stress on it.
A malfunction at the junction -------------------------------------- Dwayne
The counter argument goes, that the live pins are protected during partial insertion with the ground pin UP... which is the longest pin... so that it makes first and breaks last....
So that in a classroom it's best to have ground pins UP so that any falling object (hair pin?) is deflected by a grounding conductor. By the time the grounding pin is out of the socket, the others, hot and return, are also disconnected.
Partially engaged power cords are ten-a-penny in America's classrooms, for someone is sure to step on the cord as it drapes out of the wall socket.
As for utilization equipment in such settings: I'd favor devices with ninety-degree cord caps.
Due to the ADA statutes, I've been raising my normal receptacle heights UP. What used to be, say, a foot -- is now uniformly at least 18" (on center) AFF.
The advent of the LaserJamb has changed my procedures. I now set the LaserJamb, first, and then use it's horizontal beacon to set all boxes to a perfectly level height.
This is especially slick in old work renovations -- where plumb, square and true are mere suggestions.