Depends on the usage. Corporate usage, whether it be used as a restaurant menu/order system, inventory control at a plant, or lord knows what other dedicated uses a business might have for it, 16G is probably way too much. No movies, no music, just business. There IS a market for the 16g iPads.
My typical viewing distance is 12 inches and my eyes are far from the best.
While I didn't think iPad 2's screen was deficient in anyway, non-retina graphics on iPad 3 really stand out. And vector graphics look much thinner (e.g., lines and boxes) on apps like Mail and iCal.
As a nice side benefit, apps like Safari can load more pages in memory before reloading.