Arbing Chinese exchanges is very difficult (particularly from BTCE) -- hence why there is a persistent spread between the exchanges. Removing large amounts of CNY into USD and outside of Chinese banks is difficult. One way to take advantage of this spread is to analyze the range of (BTCCNY/USDCNY)-BTCUSD. When at range lows ($4-6 under spread), buy BTCCNY, transfer out and sell for USD. When at range highs ($4-6 above spread), buy BTCUSD, transfer out and sell for CNY.

But when your accounts become heavily outside of equilibrium (i.e. you cannot buy either BTCCNY or BTCUSD), you are stuck until the spread reverts to the mean and you can transfer out without losing profits.