After nearly 16 years of my CD collection's life, I've come across my first case of disc rot.
I'd tried to do a backup of The Sisters Of Mercy's Floodland, and it got to about 85% and then ImgBurn's speeds slowed almost to a halt (especially so after the 93% mark), and then took nearly another half hour to finish. According to the report, it finished successfully, but the end result was that that portion of the Wave file was not okay.
I decided to try backing it up a few days ago in response to this. I needed to time myself for about 10 minutes, but without a stop-watch or other easily portable means of doing so, I decided to just play "This Corrosion" and see how much I could get done. It was when I got the disc out that I noticed three or four tiny, pinprick-sized holes that the light behind it came through - something which I feared was disc rot, but only confirmed this morning after reading a more thorough description of the topic that explicitly mentioned that particular symptom.
Thankfully, I had backed the disc up several years ago, but I was unsure if the method I'd used then (using Nero to save the disc as an NRG file) was as reliable as the one I'd been using more recently (bypassing disc images and just ripping as WAV/CUE). Turns out that that part is okay, so I used the NRG backups to redo both Floodland and Vision Thing with my current method (note: I haven't checked to see if the original CD for Vision Thing is suffering from it too; the backup for it just happened to be on the same DVD-R as the backup for Floodland).
Not that this doesn't make me concerned about all the other CDs I have that I've yet to back up, particularly those that are from the 80s. I'd been meaning to go back through and properly backup all my CDs, and this only intensifies my desire to do so. And make sure I have some M-DISCs to burn the archives to.