[vgt]

Have you looked at Google's Preemptible VMs? The big difference is that it's a flat 70% off fee, rather than a volatile market, and Google has relatively few but versatile VM types, which makes it easier to architect infrastructure (ex. no need for a high-IO VM or a high-network VM.. just attach a high-IO disk to a regular VM and networking is world-class).

[vosper]

We're heavily integrated into the rest of the AWS system, it wouldn't be worth the engineering effort. Also, the spots don't make up a large enough portion of our overall AWS spend, if we wanted to save money there are other things we could do that would let us stay on AWS (which we like).