To reiterate what dpunisher already said, redundancy, redundancy, redundancy.
Flash drives are just as good as anything else for backups. But it's always good to have a backup for the backup.
Take my setup for example: Nightly, I backup all my favorite files (documents, projects, e-mails, mp3s, movies, programs, settings, etc.) to an external USB drive and to a NAS device in the closet.
Every week or so, I take the external drive to a friends house and swap it for another external drive that has the previous week's backups on it (there are four external drives here, two for me and two for him, we store each other's backups, you see.) This creates a situation where the only thing I have to worry about is the entire city slipping off the continent into the Pacific Ocean. In such an event, my mp3s would not be foremost on my mind anyhow.
In ordinary circumstances, I can simply restore files from the external drive or from the NAS. If those fail, I can restore from an (at most) week-old backup at my friends house.
All this may seem a little excessive, but I really like those files that I'm backing up.
Edited by Amazing Andrew, 18 January 2009 - 03:41 PM.