I agree with the mechanical failure issues.
However, I'd still recommend a hard drive over a set of CD-Rs.
Backups are only good if they're recent, and people only make backups if they're easy to do. Backing up to a hard drive is easier (connect drive, open app, click 'sync') than backing up to CD-Rs, which required burning and ejecting a few CDs.
However, I'd also back up your most important stuff to CD-Rs too, as a failsafe. Ideally store it offsite, like ata a bank or another member of the family's house.