I've just been "sorting" my CD/DVD collection.
The older media I purchased between 2000 and 2005 has begun to degrade badly.
If anyone has any crucial data on any older media, I'd suggest you give it whirl if you haven't for sometime and make sure everything is OK.
If you are UK based avoid Tesco branded CD-Rs. I've had some for under a year and they are already turning transparent! That's 20GB of TechNet downloads!
On the flip side the following older media of mine appears to weathering it's age well:
Orange BulkPaq DVD-Rs (4x speed),
Grey Quazar coroprate branded DVD-Rs (4x speed - bulk bought cheaply after they entered administration),
Datawrite Silver CD-Rs (48x speed),
Bulkpaq Silver CD-Rs (52x speed),
TDK Metallic CD-Rs (52x speed),
Purple BenQ CD-Rs (52x speed)
My current media of choice, which is currently available, and appears to age well are:
Datasafe Silver CD-Rs (52x speed),
Memorex Silver DVD-Rs (16x speed),
Datawrite Blue DVD-RS (16x speed),
AOne White Dual Layer DVD+Rs (8x speed),
Datawrite Titanium DVD-Rs (16x speed)
I recommend the above as age resistant, direct sun resistant, and cat resistant media!