The idea of being able to "rent" a supercomputer at a moment's notice (relative to buying one, at least) is interesting. Makes one wonder; what % of Amazon's capacity is this; and how high up the Top500 would all of it be?
It would be interesting to have a super computer config in one's EC2 portfolio for the quick CFD run, or animation sequence.
It is the latter which I find an interesting question. How hard would it be to create an 'on the fly' CGI studio? Something where your artists and their workstations are around 24/7 but when it comes time to render you pop it off to EC2 and just bill the studio for the time. That could be pretty disruptive in that business.