Geva Perry, from Thinking out Cloud, had a great post last December regarding AWS spot instances prices (bidding prices where charge is done based on market current pricing) and why the spot instances pricing should not be higher than on demand instances. The post had a comment thread by James Watters, Guy Rosen, Shlomo Swidler and me discussing why spot instances pricing should not surpass the on demand instances pricing, and why this assumption was broken (for relatively short spikes) in the reality.
NOTE: Please find my previous post regarding spot instances for more information.
