Digital BW, The Print

Steve -- In a CD, the data dye layer and the reflective layer are on
the top / label side of the disk and more subject to physical and
chemical and light damage. Triple true in "bargain" disks. DVD has
those layers sandwiched is plastic. Hence more robust. 
Think floppy disk and you'll see that we mostly have to worry about
the media outlasting their popularity, and not real archival quality
like we're usually talking about here.
A related issue, worthy of its own thread, is my great fear that the
primary legacy of the digital photo revolution will be total disaster.
We've all heard stories of folks running out of their burning house,
leaving jewelry and heirlooms behind, clutching the family photo
album. The thing they can never replace. I see a huge demographic
trusting their priceless family memories to extremely transient media.
I reckon the fraction of folks backing up their digital photo
collection to reliable media is vanishingly small. ALAS!