[eterm]

Break any and the value of bitcoins will crash hard.

You can't take millions out of a system which doesn't actually have millions worth of liquidity backing it. The total worth of all bitcoins is actually far smaller than the market capitalization of all bitcoins because the trade of them is based off an assumption that many if not most coins are dead coins.

[qnr]

Well, MtGox monthly volume is over 1 million BTC [1] or $100 million at current prices. I think you should be able to take out at least a few million without raising suspicion

In case of SHA2 compromise in particular, generating, say 20% of daily blocks would hardly be noticed (and can be easily explained as a new shipment of ASICs). This is about 720 BTC or $72000 daily.

[1] http://bitcoincharts.com/markets/mtgoxUSD.html