I can vouch for CD-Rs dying over time. I bought my first burner back in 1998 (2x, SCSI, cartridge based clunker), so we're approaching almost eight years. Probably about half the CDs I've tried from that era have issues. The old dark blue Verbatim CD-Rs seem to have the best survival rate. The no-name cheapos are nearly completely unreadable, or at least have severe corruption. For the most part, I migrated everything I needed forward, but the failure rate is alarming.
Obviously high temperatures aggrivate the problem. Typically the burned CDs I keep in the car don't last more than six months during summer heat.
So far, my burned DVDs seem a bit more stable. That may just be because they're younger, or maybe the dyes are better, I don't know.
If you need some really, really dry reading, NIST published this study on media stability about two years ago:
[www.itl.nist.gov]
It's interesting reading, in a geeky, technical kind of way, but it's not terribly helpful in selecting what you should use.
I haven't gone to archival media yet - I just use disks that aren't the really cheap, no-name media. My entire archive lives on a hard disk array, and the optical media is just a backup. Since I make a full backup every six months or so (yes, that's about 70 DVD-Rs now), I don't worry too much about any individual backup going bad in that short of time. The full backup is only a secondary backup anyway. It's only there if I can't restore off the weekly backup to an external hard disk. It has happened - I had a disk that was silently corrupting data one time, and I wound up going back to the full DVD-R backup about a month prior, which were free of corruption. Fortunately, everything from the time in between was still on my laptop.
