@jibble: So you're saying you want to create an autonomous wallet for all tradeable cryptocurrencies and then code that into ethereum scripts which then copies your wallet across the globe. You'd better be damn sure not a single one of those copies figures out how to get your private keys then or your profitability will end up being very short lived.

Also think about trading speed, you're going through several layers each with their own problems, quirks, bugs and latencies. Honestly I very much doubt an interpreted language with the added lag of global distribution and the blockchain-security-model will be in any way competitive with compiled solutions like for example the one being built into NXT, let alone the optimized solutions with ripple like speeds such as bitsharesX (novel solution for an exchange that could possibly work on bitcoin as well, albeit more slowly) promises to deliver.

Even the fastest ones of those will have some serious trouble matching the speed and trust of the existing exchange and bank systems in the eye of the general public. Plus Ripple and OpenTransactions will work just fine for the current existing financial systems, still not as fast as centralized solutions, but faster than just about any blockchain solution out there. (just to be sure, I don't own and I'm not involved with Ripple or OT).

@Equate: Agreed.