I hadn't expected the storage media question to be so controversial!
Another point to bear in mind (for long-term planning), is that recording media change !! There are many horror stories of firms and governments carefull collecting and saving data on magnetic tapes and punch cards -- but the necessary equipment for reading them isn't being made any more !!!!
So keep a weather-eye on technical changes, and be prepared to transfer your collection of CDs and DVDs onto whatever the newest "standard" recording medium is, every 10-15 years !
I have to admit that I've had many CD failures, having once worked in a small software development business.
At the same time hard disks are also not immune from problems:
a) Obsolence: as mentioned above, this is a biggee. I have some old 5 inch floppies with my old law notes on them somewhere in the garage
Hope I don't need them in a hurry.
b) Damage. My brother went out one raining day and arrived home to discover his computer totally zapped by a lightening strike. Hard disk smoking! Oh the humanity.
c) Theft.
Considering all the above, I'm thinking that I will back everything onto CD's x 3. One copy for me and send the other two off to siblings for safekeeping. I'll ask them to copy them onto their computers to be double safe.
I'll review and rewrite the CDs every year. This needs doing anyway because of the amount of new photos I'm always receiving from distant cousins. I discovered two weeks ago that one CD backup from two years ago was only partially readable. My good luck I still had the photos on my hard-drive.
I will also set up an auto-backup routine from my main hard drive to my slave hard drive. A poor man's RAID. (Last upgrade I couldn't be bothered copying everything over so I just had the old hard-drive installed as a slave drive.) You would have to be very unlucky to have two hard-drives go bad.
I'm going to be very very busy.
Leonie