Arbitrage is possible, but a lot more profitable while exploiting the altcoin market pairs rather than the fiat pairs. The best way to do arbitrage is by finding certain trends on one market between two exchanges, it could be LTC/BTC between Cryptsy and BTC-E etc. While analyzing and finding such trends, you just make sure you have big enough buffer on each market in each coin to cover the withdrawal fees (+ your profit %) when you need to balance the two exchange funds. Sure enough, the bigger buffer you can afford, the longer time between balancing which will boost your profit %, since you'll have to pay less withdrawal fees. Trading volume is also extremely important while analyzing the market for trends. No volume = no profit, regardless the arbitrage percentage.
At the moment I'm setting up a site, which will showcase arbitrage opportunities on more than 50 market pairs between 13 exchanges, totaling over 500 arbitrage calculations showed in real-time. Stay tuned!
Arbitrage between crypto pairs ,seems interesting.I never thought about that.I was thinking about crypto/fiat arbitrage.Keep us updated about your site.