Do I need to backup my Amazon S3 bucket?

If I store critical data in an Amazon S3 bucket, do I need to keep a backup copy somewhere else, or duplicate everything to a second bucket? I searched high and low for an answer to the question, and couldn’t find a definitive word. I guess I should have read Amazon’s own design requirements first…

Amazon S3 was built to fulfill the following design requirements:

[ … ] * Reliable: Store data durably, with 99.99% availability. There can be no single points of failure. All failures must be tolerated or repaired by the system without any downtime.

So there you go. Amazon S3’s massive infrastructure acts as a backup unto itself. If you store data in a bucket, it’s already being duplicated behind the scenes. Good stuff.