harley: CD's can go bad - mostly CDr's, rarely professionally pressed CD's. Depends on the quality of the CDr's that you buy - how much stress is put on them (like when they are in the case and you push down in the middle to get it out - it also puts "stress" on the disc which can cause the glue between the layers of the disks to start to give out.

Couple stories about it:

http://www.usatoday.com/tech/news/2004-05-05-disc-rot_x.htm

Plus a story which tries to paint a beter picture:

http://www.mscience.com/faq30.html

My opinion: I would rather be safe then sorry with my archived data.