The problem now is with the huge appreciation in value of bitcoins, nobody will use them as a currency since they make a better investment. People will hoard them until the price stabilizes.
They wouldn't sell them on a market so there won't be an impact on your bitcoin price. Why? Because, using Mt. Gox as a depth of market indicator, once they sold 16,000 coins the price would drop to $2.51 a coin.
Excuse the back of the napkin calculations since I don't have the full depth of market, but let's say that if they were to sell double that, say 30,000, then it's logical that the price would drop another dollar to $1.51. Extending that logic, somewhere around 50,000 coins sold would make the BTC worthless. Realistically, if the sell-off happened many more people would sell and the price would hit zero *fast*.
No, they won't sell, they have to sit on them and greedily rub their hands together. Have faith that everyone with greater than 5,000 coins will not sell (visibly on the exchange) since the realized value is not as high as the current value.
They have to sit around until a lot more money comes into the market before they can safely liquidate without destroying the goose that lays the golden eggs.
The blocking is a bit more aggressive than catching those hammering the site. I'm blocked on my home IP on which I checked the site perhaps once per hour.