Only the geeks traditionally worried about this stuff, but we always tend to assume that various types of media will be usable for many, many years.  This is not the case.  As you probably know from looking at old family photos, they don’t survive well over time.  This is also the case for tape backup (well, putting aside that even a week after it’s written, the odds are pretty good that you’ll have issues restoring from tape – I always did).

I ran across this neat diagram that shows various kinds of media, and the expected life spans.  I thought it was neat to see this all in one place.