Patch and forked s3cmd (r437) project available on github. Hopefully these changes get merged back into the trunk for the next release.
http://github.com/pcorliss/s3cmd-modification
--parallel Download and upload files in parallel.
--workers=WORKERS Sets the number of workers to run for uploading and
downloading files (can only be used in conjunction
with the --parallel argument)
The original project can be found at s3tools.org
