Well, obviously I didn't mean that DVDs would last forever, but I trust them more than a hard drive for short-term backups. Discs will degrade over time, but a hard drive can crash anytime it feels like it. And depending on the brand, your chances of recovering your data can vary quite a bit (for example, at work we'll sometimes save one by switching the electronics with an identical drive).
But Peardian is right that multiple backups on different medias is best. I use DVDs and USB sticks myself.
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Current projects: Bucky O'Hare (NES), Metal Storm (NES), Clock Tower (SNES), Ristar-The Shooting Star (Gen), Sonic The Hedgehog (Gen), Sonic CD (Sega CD), Mega Man Zero (GBA), Battletoads (NES)