Having done the math on this project in a previous life, I would also add that having to run app logic on EC2 instances and the outbound network costs are the true financial killers for S3.
S3 raw price-per-gig is somewhat competitive with what Dropbox built, but the ancillary things around it are not remotely competitive.
S3 raw price-per-gig is somewhat competitive with what Dropbox built, but the ancillary things around it are not remotely competitive.