Digital music: two-to-five year life span for burned CDs?

No real way to know

I would stay away from tape, particularly if you live in a very humid climate. I lost all of my floppies, Zip tapes, and VHS tapes to humidity in Hawaii because they became mildewed. Then the mildew on the tapes destroyed my floppy drive my camcorder, and my VCR ( could have had the heads cleaned on that).

I just checked on a 6 year old Memorex CD-RW and it works fine (even though RW's are known to be somewhat flakey). It was kept in a jewel case in a vertical position and only used one time until tonight. Also tried a very cheap (Free after manufacures rebate and store rebate) CD the manufacture of which I have no idea - came on a spinal of 100. It was also the same age as the memorex and kept in the same condition and accessed only once before tonight. It worked fine.

Because CD's are so cheap, my suggestion is that if you have some archival material that you really don't want to lose or can't afford to lose, then every 3 or 4 years burn a new copy and throw the old one away.