All hard drives will eventually fail too, though. How long will the best Taiyo Yuden or Verbatim media last, like 10 or 20 years? IMO it would be good to do both optical and magnetic backup, in case either fails. If you download a lot of DVDs, that is a lot of hard drive storage space that would be needed. When Blu-Rays become more common place, they are 25 GB (single layer) or 50 GB (dual layer). For 20 dual layer high definition video Blu-Ray shows, that's 1 TB of magnetic storage needed. One Terrabyte is probably enough to store one band's entire circulating catalog (or the catalogs of several small bands that didn't do a lot of touring) @ 16/44.1 FLAC. But when you get into 24/96 audio, DVD video, and esp. high definition video 1 TB will be spent quickly. Here is an interesting article about a scientist who is developing 50 TB DVDs, which they claim can make hard disks obsolete:
http://in.tech.yahoo.com/060708/139/65pz8.html