Apparently this has been in debate for many years, and my relatively light Google search didn’t find anything conclusive (though I found a SDMB thread that touched on it!)
Half of the receptacles in my NJ home are ground-up and the other half are ground-down.
These days when I replace an outlet, I put the pin on top, because it is easier to plug stuff in by aligning the ground pin first, and because the rare metal thing that drops on a slightly pulled-out plug will hit the ground pin.
So what is the answer in 2011? Is this finally codified, or are we allowed to choose personal preference?