So one EC2 server might be drasticatlly slower than a raspberry pi, but isn't part of the attractiveness of cloud services like EC2 that there's replication and load balancing with no headaches? now if you build a modular, distributed load balancing replicated network of 10~20 raspberry pis, that all outperform the EC2 servers... that might warrant replacing EC2 with raspberry pis.

That actually sounds like a pretty awesome project... I might do that some day.