OK, so I may have been premature as Google pop up and wipe out a lot of emails (not irrevocably as it turns out), albeit for a tiny percentage of their user base. Now this wouldn't affect me, I use an email client, so have local copies, but as the plan seems to be to get everything into the cloud, including apps, this could have been a killer. It shows even mega-corporations can't be trusted to keep the system running smoothly.
Imagine being a business and not being able to access any of your email, or a parent who just lost all their photos. Thankfully Google had backups aside from the redundant data centres (which did nothing for them in this case). Interesting that they ended up relying on tape backups! Just how many tapes is that? There must be a better solution out there.
Anyway, just because you've outsourced your data storage to a professional doesn't mean they're going to protected it any better than you can and you're in their hands when it goes wrong. That 99.9% SLA doesn't mean much when they give you back the pro-rata'd costs for a week's downtime to compensate you for all the business you lost, or all the memories that are now gone.
Never underestimate the importance of keeping backups.