Amazon promises reliability, redundancy and high availability for it's Simple Storage Service. It's unlikely that Amazon is going to lose your data. Despite all that goodness, you still need to backup your buckets to prevent accidental or malicious data loss, or just to help development.

The best tool for manually duplicating a bucket I've found so far is S3SM. It's a GUI for managing your S3 data, and it lets you copy and paste buckets without having to download their contents to your local machine - all copy operations run in EC2. Awesome!

I'm an automate everyting kind of guy, so I'd prefer it if Amazon gave me a sweet RESTful API to this functionality too. Until then, a ruby script like this is a half-way house...

http://snippets.dzone.com/posts/show/4935

Unfortunatley it downloads data to your local drive first, but useful nonetheless.