Problems with CD's
IMO: It should be stated that most of the problems with CD media are primarily due to improper handling. The format itself is very durable and lasts longer, with better fidelity than tape or vinyl. :)
First, the difference between read only silverback CD's, and recordable media: With a regular read-only CD, the pits are stamped (or etched somehow) onto a mirror-faced, perfectly flat piece of thin metal
Second, why skipping occurs: Skipping occurs when the CD player's error correction recieves bits that it doesn't recognize as audio, and can't correct them by oversampling the data and interpolating the results.
Third, what actually causes skipping: Effectively, the pickup head (a photo-transistor) isn't getting proper reflections from the CD medium.
Fourth, CD's are designed to last aproximately. 10 years. While they may last longer (My copy of Information Society's first album is over 11 years old, and plays fine!), they still might be degrading enough to where data can be lost that can't be recovered. This is mostly a problem with data CD's, as error correction on most audio CD players can cover up subtle anomalies. Still, "your great CD collection isn't going to last you all your life no matter how well you treat them." -- Oeq1st1
Common Medium Errors:
What causes the head to misread or not pick up laser reflections:
1) The most common problem with both read only and read/write media, is that the plastic surface contains gratuitously large imperfections that cause the laser to reflect to an area other than the pickup head, or not to reflect at all. Generally, the type of scratches that cause the most difficulty are scratches that are arc shaped, and have a fairly uniform radius from the center of the disc. Since the data stream is corrupted for such a long period of time, the error correction can't interpolate the data, and thus, it skips.
2) The other problem is that the reflective layer has scratched away. In the case of read only CD's, that data is gone forever. In case of read/write CD's, the data is still there, and accessable if it's worth going through the troubles fo doing so.
If the first problem is what's causing the skip (visual inspection of the bottom of the CD will confirm this), you can use a scratch filling product to fill in the scratch, then buff it out, thus causing less scatter of the laser. The idea is not to perfectly restore it, but to get enough reflection so that the error correction can make up for it.
If the second problem is the cause, (This can be verified by holding the disc with the mirror side towards you, looking directly into a bright light, and checking for any bright spots) then you're S.O.L. if it's read only. If it's read/write, you can carefully apply spray chrome paint to the top of the disc, carefully shielding the rest of the disc with sponges, towels, etc.
None of these methods will work 100% for every problem, and the degree to which they work is inversely proportional to the size of the damaged area. ie: If half of the reflective layer is missing, forget it.
Also, these solutions are not designed to be permanent! If you value the data on the disc, use your magic to fix it, then replace the disc, or duplicate the data onto a new disc.
Myth: You need to clean your CD player lens frequently.
Fact: Wrong, repeated cleaning lessens the overal effectiveness of the lens. Think of the brushes as fine-grained sandpaper. (most of the brush based systems are basically that) No matter how soft, or fine the grit, it will still add imperfections. These build up over time, and result in an unusable CD mechanism. Liquid brush based solutions are just as bad, if not worse, since they're more likley to be improperly used. Also, does wet sandpaper sound any more appealing to you than dry sandpaper?
Myth: CD's are resistant to the heat of a car on a warm afternoon.
Fact: My car reaches aprx. 135 deg F if left in the sun on a 95 deg F day for more than 45 minutes. At this heat, the glues that hold the layers of a CD together begin to decompose. Not completely, and not every time. But over time, this constant break down and re-building of the glues will cause problems, such as the reflective layer peeling off inside the CD player. I've lost several CD-R's this way, and one car stereo. I could see the overall color of the dye layer darkening on CD-R's if I left them in the car for a couple of hot days in a row.
Added section about lifespan of CD's. (Thanks, Oeq1st1
!) Corrected (I think) a couple of singular/plural ambiguities. (Thanks, wharfinger
Added part about arc shaped scratches. (Thanks, WolfKeeper