If the Earth radius was 100 pixels, the average depth of the ocean (~4km) would be less than 0.1 pixels. I once had a professor hold up piece of paper and say "this is my scale model of the pacific ocean". Took me a while to realize he wasn't joking.
The one my teacher used was the billiard ball, and told us "if the Earth were the same size as this, it would be smoother". A quick google suggests that is indeed true, but it would not be rounder. (http://blogs.discovermagazine.com/badastronomy/2008/09/08/te...)
