According to what I read on boxes of CD-RW media, the Rewritable CD has a life expectancy of 1000 writes.
When I got my first CD-RW drive some years ago (when they first came out), I asked HP customer support about the longevity of CD-RW media. They told me that the 1000 times was basically an estimate. He told me that they had done their own trials and discovered that they last even longer. They hooked up a drive and created a program to write and rewrite to the same sectors on the CD and after days of running it had not produced any errors.
How long can a CD-RW last?
How do you know when a CD-RW is no longer reliable for storing data?