This is quite interesting. I had just built a predictive rebalancing bot to trade on MtGox a few hours before it collapsed. I was rebalancing every 60 seconds and making lots of trades. I only got a couple of hours of run time before it stopped working :(

Here's the bot I built: https://github.com/pontifier/rebalancer

Quantopian looks interesting, and hopefully the exchanges it trades on won't disappear.