They are DVD+R, burned with a standard setting in Nero 6, no-multisession. I've never had a problem burning a DVD before. I was suspecting that Nero 7 was acting up with burning CD-Rs, so I downgraded to Nero 6, burned a few data DVDs while at it, only to discover that none of them are readable. And since I've built up some trust for the Nero-made DVDs, I didn't bother verifying before Shift+deleting my files.
Both of my computers take eternity to read the disks with no end result. Same story goes for IsoBuster, which isn't able to make an image. The only other peculiarity that I've noticed is the larger than normal indentation from the center on each disk.
Thanks for looking into this