First, we learn that cloud services aren't fool-proof. Too many folks expect perfection, and, as Robert Burns said, "The best laid schemes o' mice an' men Gang aft agley." For those who don't speak Gaelic, that's, go oft awry. All technology services will fail occasionally. The question you should ask before signing up for hosted e-mail is, Can the hosting provider keep my e-mail working at least as well as my current Exchange administrator can? In my experience, the average Exchange installation has a moderate-size service failure about once every 18 months. Gmail seems to be doing at least that well.
This event affects about 40,000 users, so it's of the scale of a corrupt Exchange information store or single server crash--the kind of thing that happens every couple of years to all but the best Exchange users. Of course, smaller systems are easier to restore, so at the three-day mark, 95 percent of those Exchange problems are over. In contrast, I have friends who still didn't have their Gmail back as much as four days after the incident.
Then we learn that SLAs protect the fees you pay your cloud provider, not the assets you put in the cloud. Like all other data, your Gmail messages are protected by backups. Those of us who believe in a belt and suspenders are not just protected by Google's tape backup but also by our own backups. I use Google Apps e-mail with the Outlook connector, and my backup system backs up the PST file with my mail daily.
Then we learned that despite the best efforts of the Tape is Dead Marching Band and Chowder Society, Google uses tape as the line of last defense. Gmail data is replicated among multiple data centers but also backed up on tape, and it's from those tapes that the data is being teased and restored.