At current rates and the state of the order book on Mt. Gox, it would take ~170,000 BTC to take us down under $10.00 - anyone doing this would net an average price of ~$19.61, which would be a total value of $3,333,700.
Why anyone would want to cash out 3.3 Million is an exercise left up to the reader, but I'd classify this as being pretty remote.
Why dump it all at once? If they sold 1,000 bitcoins a day at $25 they'd pull in $4.25 million...which from my perspective is quite a bit better than a measly $3.33 million
(a lot is being assumed in this situation, but still...)
Maybe they're willing to sacrifice a million because they don't want to wait an extra 169 days? ..meh, who knows..