The moral of the story is that, at the current difficulty and bitcoin price, rented server instances are not profitable to mine any coin. But if the price were to continue to skyrocket, or there were to be a drop in difficulty, it is an easy thing to set up and try.
Maybe you should try to mine a CPU only coin rather than scrypt coins if you're going to try an amazon ec2 instance. There are plenty of CPU minable coins to choose from quark, protoshares, xpm etc. In my experience cloud hashing on these coins (though not at amazon) has been slightly profitable, and a small profit per instance could be scaled up to a large profit with many instances. Saying that it is not profitable to mine any coin this way is not correct, it is only not profitable to mine scrypt coins this way.