Do you have any evidence for these claims of low durability?
(None of those issues, except for bugs in the service, would count against them, by the way.)
1. Amazon claims 99.999999999% durability of objects over a year.
2. I store 1EB of data with an object size of 4MB for a year (so 250,000,000,000 objects).
3. I can expect to lose 250 objects in a year, or 1GB.
Now to my experience:
I have stored in excess of that amount of data in S3. I have lost considerably more data -- solely because of data losses internal to S3 -- that these numbers would suggest. It was a tolerable amount of data loss, I didn't curse Amazon's name or swear vengeance, but it was definitely not 1 gig.
The standard S3 SLA provides credits only based on uptime. There is no mention of durability whatsoever. That tells you that Amazon is not willing to put their money where there mouth is on their 99.999999999% durability claims. The reality is the number is a design target, not an operational guarantee.
I didn't use SNS notifications at the time (which might only work for reduced redundancy).
So that left two options: find out when attempting to fetch the object, or run bookkeeping jobs against the object catalog to periodically spider the data and ferret out any objects that are lost.
The second option may be a tad nicer, but it is also more complex and more expensive and the end result is the same either way.