Just in case it helps anyone: I picked up a pair of LG GSA-H54L 18x DVD-R burners from Fry's yesterday. I returned them today.
I'm using Nero 8 to burn TYG02 media at 8x. The H54L works fine, and produces good scans, IF I only use one burner at a time. They always fail if I burn using two drives at once (first error shown is "No seek complete"). I have been burning using two drives at once, with this system, on this media, using Nero 6.6 for several years now with no errors, so I doubt it's my system. DMA is enabled. One drive is a master, alone on a separate IDE channel. I have a separate EIDE card just for the second burner.
I looked for updated firmware, but was unable to find any firmware anywhere for this model. Before trying the LG drives I had been running a Plextor PX-712A and a BenQ DW-1640, and they worked fine when burning at the same time.
fwiw, I started burning DVD-R in July 2001 with a Pioneer DVR-A03 and have run through some thousands of DVD-R and quite a few burners since then, generally without problems so I don't think I'm doing anything drastically wrong.