As soon as the other exchanges become more liquid there will be more opportunities.  I am not sure about all of the exchanges but most of them do not allow money to move BETWEEN members accounts.  There are reasons for this of course, but because GOX allows money to move between members (in USD) the site becomes even more liquid. 

Dwolla in other exchanges will make the more liquid as well. 

+1

and also, it is difficult to move money in/out of most exchanges at this time, because they are small.

Arbitrage is there, but you must understand all fees involved in the various exchanges fiat currencies etc.

No, because the only way to profit 'risk free' is to get the funds over to the other exchange before a price change takes away the opportunity.

Yes, this is the way.  It takes bitcoins to make bitcoins    Have ready money in multiple spots and buy the underpriced coins, move them to the better market and sell them.  It will also in the end help regulate price.

What do you mean?

According to your first post, "Suppose on Bitcoin exchange A, you can sell your BTC for $5.50, but on Bitcoin exchange B, you can buy BTC for $5.30 each. So you buy up all the BTC you can on exchange B, transfer them to exchange A and sell them all for instant profit."

If you already have balances at exchange A and exchange B, you can simply buy the BTC at exchange B and sell your BTC at exchange B at practically the same time. You profit without having to transfer. The only problem is you have to hold balances of BTC and other currencies at the exchanges.

Are you looking at the actual order books or the last trade?

I created a trading robot to do this, but it could never work on a large scale because the exchanges wait for transactions (edit: Bitcoin funding transfers) to be confirmed (which takes time) before crediting your account. Holding both BTC and USD in both accounts leads to larger losses due to price changes. The whole point of this type of arbitrage is that you must be able to transfer the asset between exchanges instantaneously to take advantage of price mismatches.

Sending orders to multiple exchanges is what a broker does. For now, anyone can have a seat at the exchange, but if Mt. Gox decided that there was some minimum account balance or a seat fee to trade directly on the exchange, then this would give rise to brokerages with seats on the exchange. This is the model of the dinosaur financial system: charge $50k/month to institutions for a seat at the exchange. They create brokerage accounts and can send client orders to the exchange or to other clients. Brokerages can give 'liquidity credits' to clients who place limit orders within the Bid-Ask spread because they can simply fill orders from other clients, not send them to the exchange.

Of course I don't want to see Mt. Gox start charging for a seat, but it would be very interesting to start a brokerage. You would be able to provide many client services that the exchange doesn't, such as shorting, leverage, liquidity rebates, multiple-exchange execution, etc.

This discussion leads into the question of whether someone is going to launch a futures options exchange. Just think, the miners could sell a futures contract on the coins they will mine, in order to lock in a price. Or you could offset your mining risk by buying an option in the case that you go into that 95% confidence level and get a way lower return than you expected.

There's an app for that!
  - http://fnoose.com/bitcoin/arbitrage - http://forum.bitcoin.org/index.php?topic=14466.0

The fourth largest bitcoin exchange in terms of trading volume, Bitfinex announced the launch of a decentralized trading platform EOSfinex, which is based on the EOS blockchain.