Jesus saves, but Buddha makes incremental backups
It can happen to anyone, at any time. Even professionals.
"I used to backup the data from that server every week, on another host. But last week, I needed some space for a specific application. And I temporarely deleted the backup. 2 days later, the disk died. And that host was always backuped for 5 years before. Call it Murphy's law or voodoo, but it really, really, really sucks."
You, reading this now. Yes, you. What would you lose if the hard-drive in the computer you are using now never span up tomorrow? Anything important/sentimental?
Never trust data to one hard drive. They die regularly randomly. (If you can say that). I'll repeat that: Don't trust hard drives.
A clever person said: "There are 2 types of people in the world. Those that have lost data, and those that will."
I suppose that there is one benefit to Open Source software - the source code to his FTP server can be found in many places. I use ProFTPd or vsftpd however.
You can always use this online backup service to make sure that your files are backed up.