Man, i'm pretty upset about this. I have a Pioneer DVR-106, the A06 (retail, not oem). I have burned many different types of media since I got it, this most recent christmas (2003). I didn't notice the problems until this week, and i've gone through my collection of DVDs that i've burned, and about half of them are rotting!
I'm not sure if the substrate is oxidizing, or what - little darkish spots are forming on the purple layer underneath, and they are neither on the top or bottom of the DVD (can be confirmed by gently rubbing a finger over the disc, and/or then destroying the DVD with a pin and noting where the darkish spot resides).
I've taken extensive pictures along with the brand names and media types of each, and made a webpage here (pics are too big to post here). Please, if you have the time, take a peek... Pictures
Since so many different media types and brands are showing the same thing, regardless of +R or -R, can this be the drive? is it somehow overpowering the burns and then this happens? It doesn't always take time to set in - one of the examples on the page given had problems 10 minutes after burn!
Note, before I burned ANY of these DVDs, these darker spots were NOT visible, or I would have just taken the media back. Also, all of these DVDs originally burned with no errors. Some can still read without a problem, others read slowly, and still others don't read at all.