Thanks, I wasn't aware of the spot pricing (never scrolled that far down the very long pricing page :)

I'm not sure that I understand the economics of the spot option from Amazon's POV since it seems that a person who needed persistent servers could set their spot max price at the same price as an on-demand instance and always be ahead by doing it that way (with the caveat that there would be a short interruption if forced to switch to on-demand).

For someone who needs cheapest possible compute power with a flexible schedule, spot arbitrage makes sense of course.