[olegkikin]

I created a script years ago that looked for arbitrage opportunities on BTC-E, up to 4 trades deep, and it used the order books properly. I left it running, and was surprised that it actually found some arbitrage opportunities, around once every 3-4 minutes. Unfortunately the profits were always lower than 3-4 transaction fees of 0.2% each, so my dreams of getting rich quick got crushed.

I'm was actually surprised BTC-E didn't do something like that themselves, since the they don't have to pay any transaction fees, and they also had zero lag. It's like free money.

[mhluongo]

They almost certainly did. Crypto exchanges will give market makers and arb shops deals on exchange rates.