Interesting question. If you have an ounce of gold you're richer than average and an ounce of silver makes you a freak!
Gold ever mined: 158,000,000,000g (end of 2006 - http://en.wikipedia.org/wiki/Gold#cite_ref-14)
People on earth: 6,000,000,000 (or more)
Grams/person: 26.333
Silver: 300,000,000 ounces (excluding the <5% that's left in the ground and the stuff that's in landfill) for 6,000,000,000 people.
http://www.monex.com/prods/silver.html