Re: Why so much difference in prices between exchanges?
The price depends on the trades executed on the exchanges. So yes you could do arbitrage - if you can move your money/btc between exchanges fast enough 
Only if you can get a decent fill. The lag times at Mtgox make that a hell of a gamble right now.
This. The risk vs return on arbitrage right now isn't very good. That's specifically because of order execution time. If everything were as liquid as forex those of us who have traded prior would be making a couple million a day pushing coins across multiple exchanges but its just too slow right now.