No. The market just isn't that deep. I really doubt there are people looking to spend 10 million (or even 1 million) dollars on bitcoin in any normal time frame.
Most of the bitcoin super-rich are the early adopters, who mined hundreds of bitcoins on their personal PCs while that was still possible.
One million dollars is less than 1400 BTC on gox at the moment. There are several transactions a day in this range.
And contrary to the popular folklore, you can get USD out of gox, it just costs you a fair amount to do so. If you're dealing in million dollar transactions, it can be arranged.
To put it in perspective, Bitcoincharts.com [1] reports that the market trade volume is around 200,000 BTC (I believe this to be a 24hr stat). BTC-China is currently the largest exchange and their 24-hr volume is 67,500 BTC. So yeah, several thousand BTC being traded at once could be a significant disturbance in the force.
I wonder if it would be possible to come up with some kind of market indicator to detect when one of major holding addresses starts to sell off on one of the exchanges. This may be possible if the escrow/intermediary accounts are known. If one of these 'major holders' really felt like being evil, they could test out some of the BTC to USD processors to see how well their setup to handle large transactions and nuke them with 1000BTC conversions. Coinbase.... BOOM!... BTCQuick.... BOOM!
It would be trivial to write a script to watch the top however many addresses for movement. You wouldn't know if the coins were headed for an exchange or not, though.
Most of the bitcoin super-rich are the early adopters, who mined hundreds of bitcoins on their personal PCs while that was still possible.