Has Mac OS X Snow Leopard made DVD burning unreliable?
It certainly has for me on my older iMac (Intel Core Duo). Some people seem to have similar problems (just google for “dvd burning mac error” within the last year), but I don’t know how widespread the problem is. For me, the main issue is that DVD+R DL disks that I used to be able to burn don’t work, any more. If you have similar problems, you should let Apple know.