> I've had HDDs give me warning, and I've had HDDs fail without any warning. People have gone to their backups and found them unreadable.
Absolutely agree here - a backup is only as good as the system used to validate it. But as we've seen since this service was mentioned, Google have already been found to be re-processing the images sent to it (I've seen mention of RAW images which were quite significantly compressed), so they're just as good/bad from a backup integrity point of view.
At least one can monitor one's own in-house disks and backups!