A deep scratch on the label side can mean you've physically lost parts of the data layer (depending on how deep). As C0rinthian mentioned, there's not much protecting the data layer; A CD is 1.2mm ...
I've got one of those CD/DVD doctor deals that I picked up at Costco a couple years ago and it has brought almost everything I've tried in it back to life. I had a disc damaged in the way you describe ...
This article was taken from the February 2011 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands ...