What should be done is setup the exchanges to trade off a common market place similar to the Stock market, Have the central exchange not exceute trades directly but make profit only through API usage. Exchange gets and API that is constantly updated with the current prices bids and asks and volumes and allows trades to be made cross exchange to which ever is offered at the prices. Instead of the exchanges looking at each other to get their cues which way the market might be heading
Interesting idea... You could have the
exchange be decentralized, but have the follow-up (actual payment of goods) be handled by the (current) exchanges.
You would give USD to Mt. Gox or someone to represent you on the market, because they are trusted and everyone knows that they already have your money if they are representing you. You place orders which are matched up regardless of which exchange the other party is using, and then the exchanges settle with each other by sending USD or bitcoins to each other every so often.
Although wouldn't this would be very similar to the current fiat banking system? I guess one difference would be that you wouldn't use them to store money, only buy and sell it for you (more like a stock broker). Also, this could just be set up between exchanges and not have to be tied to the bitcoin protocol at all.
Like coqui33, I too have seen lots of calls for a decentralized exchange, but I don't see how it could be possible without being extremely hit-and-miss in terms of trusting people to wire you USD directly after making a trade...