Early in my career, I became the second person able to support and operate a system that was public facing and responsible for billions of dollars of activity that mattered to many individuals and stakeholders. The entire team retired over a period of six months, after giving the folks in charge a year or more notice. After about 12 weeks, I was the sole guy, training a 4-5 new people.

We’re all probably using a service like this. As demonstrated by Twitter, well engineered systems can persist, even without proper care and feeding, until they don’t.

That is to say, if Tarsnap is the only place you've keeping sensitive/important data, then you're "not doing it right" as a backup. Things happen... your hard drive can die suddenly, and a data center bursts into flames all on the same day.