Conventional wisdom keeps flip-flopping between ground up or ground down. The NEC (national electric code) is silent on the subject, except at one time they did require grounds on "critical circuits" in medical facilities to be up, to avoid blowing the breaker if something fell and contacted it. For whatever reason, that spread and became the 'norm'. But lately, its moving back to the conventional way. I'm guessing that electricians are getting tired of callbacks due to people complaining that they are "upside down".
Feel free to put them in however you feel, there is no right or wrong way. I myself put them in with the grounds down, as I have seen some electronic equipment with "wall-wart" power supplies that have polarized plugs (that only insert one way) where they would be upside down and more prone to fall out if the outlet was ground up.
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