I looked at this with Bitstamp and Mt Gox, where the price difference can be 7-8 USD. This has happened on the last two weekends, and will probably only last while Mt Gox has issues with USD withdraw. Maybe this will be resolved soon as they have registered in the US as a money transfer business.
E.g.
1. Buy BTC at say $100 at Bitstamp, transfer the Bitcoin to Mt Gox, sell at $110.
2. Now wait 2 weeks for Mt Gox to transfer your fiat funds, so you can repeat the process.
After accounting for bank transfer fees, currency conversion fees (your profit is in USD but I have a GBP bank account), the return would be less than 5% per transaction I guess. Break out a spreadsheet.
Andy.
https://support.mtgox.com/entries/21649594-Withdrawals-and-Deposits now says 3 weeks for SEPA withdraw.
Some working out with a spreadsheet shows that in a 100 buy at Bitstamp / 105 sell at Mt Gox arb, accounting for exchange fees and the 1% SEPA withdraw fee at Mt Gox, the net would be $3.83. If you did this arb with 10K USD then it might be worth it.
There is also a step 3. Move fiat funds back to Bitstamp, and there will be a bank transfer fee here as well.