Does the 2008 NEC specify which way to orient 3-prong outlets?

Should it be

ground on top
http://upload.wikimedia.org/wikipedi...with_label.jpg

or

ground on bottom
http://images.jupiterimages.com/comm...4/23433400.jpg

?

The tradition seems to be ground on bottom, but I heard it is safer to have
ground on top so falling coins are less likely to short out a loosely
plugged in plug.