We're a big fan of using spot instances in Amazon's infrastructure. It allows you to basically bid for the market against the market price for compute. Spot instances are really good for when you want to spin up some stuff, do some work for 30 minutes and throw them away. And at least in our case, because the backend infrastructure is fault tolerance, if the market price happens to change and you lose the machines, you can just go and raise your bid price or wait for the price to be up again and continue where you're left off.