Yes. You should adopt a backup policy that assumes we are storing crates of sweaty dynamite on top of the servers that hold your important data. (Even though we aren't.)
We perform automatic rolling backups to protect live website data, and extensive multimirroring for MySQL data. (Which, incidentally, explains a big chunk of our storage charge.) In the event of a serious catastrophe, the most harmful consequence would probably be the loss of everything since the most recent backu.
That should not trick you into thinking you do not need to make your own backups early and often. If we actually had to restore backups from scratch, the amount of data involved is very large and it would take a really long time, during which you might want a copy of your data.
You should also keep your own backups in case you make a mistake while editing your site. People often send in requests for help recovering files they accidentally changed or deleted. Our backups are designed to recover the whole system, and they are designed to discover and back up changes as quickly as possible; this policy of "disaster recovery" focus on current data actively works against the use of our backups to recover old or overwritten data.
Sometimes it works. If you let us know right away, we will try to help. But for the same reason the chance of losing data in a disaster is very small, the chance of getting back old versions of changed data before the change itself is backed up is also very small. You shouldn't count on it. In most cases, we will need to charge you for the sysadmin time and resources needed for a successful recovery based on the amount of data to be restored and the amount of effort require to restore it.
Make your own backups, please! We are happy to try to help, and we love to save the day, but it stinks when we have to tell someone that we can't help them get their hard work back.
