Recently I've had a few people ask me about archiving and storage media... Here's my thoughts:

Hard-drive vs. DVD/CD. I come down firmly in the "back-up and store on DVD-R" camp. My reason is simple: a high-quality DVD-R will last you between 75-150 years... You're lucky to get 5 solid years out of a hard-drive and that's with semi-frequent use (you have to keep the disc-head and platter in use or they will start to stick). If you don't touch your hard drive or even turn it on for 4 years, it might not boot up at all. A DVD should last you long enough to transfer the data to whatever new storage media emerges over the years to come.

This goes for archiving your music too. And it's also not a bad idea to consider storing your stereo mixes as 24 bit files... for the day when all music is DVD audio quality (24 bit, 48 Khz). Who knows, you or someone else may just want to re-issue the re-mastered version of your future classic 25 years from now.