OK, I jumped onto the breathtaking USB 2 train with my external LaCie DVD drive, since chances of having a minimally reliable FW400 connection were scarce (see above). The result is I can burn DVDs - slooowly, very slooowly - but during the subsequent data check an error pops up inevitably: Sector xx is unreadable, check failed etc.
Luckily, the DVD is OK when played.
Has anybody noticed anything of the kind?
Ah, the news is I upgraded to Mavericks. Though it happened the same, before (10.8).