picolo, you're right, but not exactly in 100%.
Problem of arbitrage is market depth. There are probably much more better ways to invest for example 200-300BTC, but i think for capital around 100BTC, arbitrage is still very profitable.
Now my capital is something like 10BTC, and i can easily make at least one arbitrage circle daily and get profit around 1% after fees.
For me most important is safe and stable profit and i can easily achieve that with arbitrage.
Does that mean you earn 3 BTC a month from arbitrage?
1% profit everyday would be even more than 3BTC/month but maybe he can't get a good arbitrage trade every day.