We've done a lot of rewiring around my commercial property, and about half of the are up, and half are down. I thought at first it depended on which person had installed the outlet, but I asked around, and it seems that what actually happened is the person who installed the most outlets just never looked -- he installed them whichever way they were when he picked them up. Drives me batty. I'm getting ready to sell the building, so I've been going around and changing the ones I don't like -- so the ground plugs are facing down. No reason, other than the way the plugs are shaped, they seem to fall more naturally into my hand, that way.