Recently a Google glitch disabled 150,000 gmail accounts. Mashable posted a backup method using some software called Gmail Backup.
However, it is important to note...Google didn't lose the email permanently. As they have explained
To protect your information from these unusual bugs, we also back it up to tape. Since the tapes are offline, they’re protected from such software bugs. But restoring data from them also takes longer than transferring your requests to another data center, which is why it’s taken us hours to get the email back instead of milliseconds.Google's offline tape backup is very reassuring to this customer. I am not one of the .02% of Gmail customers who woke up a couple days ago to empty accounts. You would have heard from me if I had been. While it may be possible to imagine a natural disaster that might impact both the backup servers and the tape backup simultaneously, I am comforted that they are not relying completely on digital storage.