The graph at: http://blockchain.info/charts/n-unique-addresses
Shows us that the total number of wallets which have had transactions during a single day peaks at about 100k. Now I have no idea if the transactions which result from a trade at mtgox is witten to the blockchain but i would guess that it is. (occams razor argument)

If we take this chart to its biggest extreme we can integrate the number of wallets and consider each of them to represent a single individual. If this was the case we would find roughly 1M people involved with trades over the last 15 days.

If every wallet which has been involved in any trade within the blockchain the last 15 days represent a person who has payed more than 70 usd on average for bitcoins and also failed to sell them at a profit then we would be looking at a total of 1M punished individuals.

Now if we filter this hypothesis through some sort of reality we might get closer to a decent estimate. ^^