Some interesting questions came in via e-mail the over the last month, so I'll cover those instead of the questions at the meeting. But if something is really important, it's best to have two backups.
All storage media is fallible.
Apparently some is more fallible than others. There have been reports of Zip disks and drives failing. It is called the Click of Death because when you insert a Zip disk the drive repeatedly clicks but never accepts the disk. The theory espoused on the above mentioned web page is that the drive gets magnetized by proximity to the magnetic fields near a monitor. I'm skeptical about that since, most Zip drives are located close to monitors, and most don't fail.