Lifespan of CDs and DVDs

How long do CDs and DVDs last? The short answer is that no-one knows, largely because the technology has not been around long enough to test longevity. Some say that cheap CDs burnt on your home computer will last only 2 years - others say that better quality disks commercially pressed will last 50-100 years. There likely is a difference between home-burnt and commercially pressed, because the process is different, but all I can report is that so far I have not had a disk die of natural causes (and my oldest are getting on for 10 years).
One thing that can cause a disk to crash quickly (and I have been guilty of this) is to write on it with a felt pen. The ink can degrade the media underneath, and bingo! your disk is unreadable. While you can buy pens which are supposed to be non-degrading, a simpler solution is to write only in the central area around the disk hole (where there is no recording media underneath). One big no-no: don't stick small labels on the disk. Apart from the fact they can catch in the mechanism, they unbalance the disk, and this can wreck a drive spinning at several thousand revolutions a minute.
It is more likely that the problem with electronic media will not be wear-out, but the changing technology of data storage. Long before the disc itself becomes unreadable, it is likely that the CD-ROM will be replaced by a new medium and that it will not be possible to find a CD-ROM reader, except perhaps in a museum. To illustrate, how many of you still have a 5 1/4in floppy disk drive, which was still quite common only 25 years ago? Librarians and archivists are quite worried about how we will preserve today's data for the future. Books can last for thousands of years, but technology has a very fleeting lifespan - who is going to keep re-archiving on new media forms as the old ones become obsolete?