Hacker News Reader

They do plain GMail too, along with a handful of other services (flickr, facebook, twitter). It looks like their emphasis is now on Google Apps. I just took a look and if you click the "social media backups" link (unintuitive), you can find GMail in there.

Data is stored on Amazon S3, according to their home page[1]. So, yeah, it's backing up one cloud to another which HAS had outages, but it does reduce risk/exposure.

[1] Features

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Nightly Backups using Amazon S3

Backupify uses AWS, if I recall correctly. Services like this will become an absolute must, I expect.