This past week, I bought some software on DVD-ROM. I wanted to make a backup copy (the discs are not copy protected, and no I am not giving any copies away to anybody else, so this is perfectly legal). There is 7G of data on each disc, meaning dual-layer media is required to hold the backup.
I went to a local store and bought a 10-pack of generic "Windata" brand media. I chose this brand mostly it was the least expensive brand in the store ($10 for a 10-disc spindle), and they were rated for 8x speed (My Plextor PX-716A can burn dual-layer media at up to 6x). I knew that this was a no-name brand, but it has the "DVD+R" logo printed on it, so it should conform to the specs for +R media and work fine in my drive.
Anyway, using this media was a colossal failure. I tried several methods to make the backups (copy with Toast, make an image and burn it with Disk Utility, copy the files to my hard drive and burn a new disc, etc.) and they all failed. Each time, I got weird errors from the drive, usually about buffer underruns, even though the drive has underrun protection. I even tried installing a firmware update from Plextor, which didn't help.
I also noticed that software was only reporting 4x capability.
Strangely enough, however, burning a 1.8G data set (which only uses one layer) worked fine on this media. Thinking there might be some kind of copy protection, I tried burning a disc with 7G of my own data - that also failed.
After doing some web searching, I found a lot of report of people having problems with Windata media and Plextor drives. Everybody recommended Verbatim.
So I went back to the store and bought a spindle of Verbatim media ($30 for 20 discs - a bit more expensive, but not too much more so). This time, everything went flawlessly. Software reported 6x burn capability, and I was able to make my backup. I made image files from both discs using Disk Utility. I burned one with Disk Utility and the other with Toast. No problems at all, and I got my drive's full 6x speed.
At this point, any reasonable person would conclude that Windata media is just junk. I did too.
Seeing my problems, my housemate, who had also bought a spindle of Windata media at the same time, decided to return his package (unopened) to the store. Just for kicks, I decided to see if I could make my backup on his computer (a generic Asus PC, with a Samsung 8x OEM drive, Windows XP and the Nero Express program that came with his drive) using some of my leftover Windata media. It went perfectly, generating no errors, and burning at full 8x speed.
So apparently Windata isn't complete junk. They're incompatible with my system (Mac and Plextor drive), but they seem to work just fine on my housemate's PC. (He kept his spindle of media.)
Conclusion: DVD media is not much different from CD media here. Although the trademarked logo may ensure that the disc is up to spec (assuming it wasn't used illegally), it doesn't guarantee compatibility with all drives. And media that doesn't work on one drive may work just fine on another drive.