I've released a new version of my S3DropBox on GitHub. I've moved the project to GitHub so that I can have all my current active projects in one place. Check it out in its new home at https://github.com/tomcz/s3dropbox.
This release uses the AWS java libraries. They are finally good enough for me to stop creating my own wheels and vulcanising my own rubber. As a bonus the S3DropBox creates URLs in virtual hosted format (eg. https://mybucket.s3.amazonaws.com/myobject) if the bucket name permits that, uses HTTPS by default and is able to perform multipart uploads so that large files get uploaded faster.