With volatile exchange rates (both in BTC and lately in the other currencies as well) and markets in over two dozen currencies, the are plenty of opportunities for arbitrage. The order sizes are generally small though so the amount of profit from arbitrage isn't enough, it appears, to attract automated arbitrage trading just yet.
I believe this is the main problem. There isn't an easy, fast way of transferring money between currencies. So if you want to arbitrage for all exchanges in all currencies, you must have a lot of money sitting idle in these exchanges waiting for something to happen. The problem is that when something does happen, you will not earn much because these exchanges have a really low market depth. It's like walking around the park picking up cents.
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