I may have to try this out - I upload to S3 a lot:
I needed a client to interface with S3 from Linux to store and retrieve archives and backups up to 100s of Mb large. Although I had already written a client for this web service in Pharo some time ago, I thought it would not be good enough for these amounts of data. Furthermore, it had no command line interface. So I Googled and found s3cmd. This installed easily and quickly in Ubuntu. Uploading/downloading some small test files went OK. However, uploading large files gave all kinds of strange errors, even though I was doing this from EC2 directly on the Amazon network. I don't know Python so I was not capable of debugging the tool.