1% price difference. Subtract trade fees. Then divide by 2 (because you need BTC on the high-price exchange and the same value in USD on the other). That's the theoretical profit if you can utilize all your funds. In reality, you'll have most of your fiat stuck moving through the slow international banking system from one exchange via your bank account to the other exchange.
If you can translate a consistent 1% price difference between exchanges into a daily 0.2% profit then you're doing an amazing job.
Apart that I used to see greater differences than 1% most of the time between btc-e and bitfinex, there is no need to divide by 2, since btc-e is all the time the lowest price, so the operation would consists just in sending fiat to btc-e to buy btc there while selling btc on finex at an higher price. [edit]: and of course there is no need to use the banking system for each single trade, just to refill the fiat deposit on btc-e when needed, which may be once per week or so.
To me it seems feasible. And probably a pro with high volumes could even obtain lower fees.
But I am not pimping. I already said to play just with anything one is willing to lose if at all.